The Diagnosis, Evaluation and Management of von
Willebrand Disease
Diagnosis and Evaluation
Introduction
The evaluation of a person for possible VWD or other
bleeding disorders may be initiated because of a variety of clinical
indications (see Figure 3). These indications and
situations may include evaluation of: (1) an asymptomatic person who will
undergo a surgical or interventional procedure; (2) persons who present with
current symptoms of or a history of increased bleeding, abnormal laboratory
studies, and/or a positive family history of a bleeding disorder; or (3)
persons who present with a prior diagnosis of VWD but do not have supporting
laboratory documentation. In all cases, the initial step in assessment should
focus on key aspects of the person’s clinical history to determine
whether the person may benefit from further diagnostic evaluation. This section
is divided into two parts. The first part uses a summary of the medical
literature to provide suggested questions for an initial assessment of persons
presenting for concerns about bleeding issues or for evaluation prior to
procedures that may increase their risk of bleeding. Using the answers to the
initial assessment, the second part focuses on a strategy for optimal
laboratory assessment of those persons who potentially have bleeding disorders
and suggests guidelines for interpretation of laboratory results.
Evaluation of the Patient
History, Signs, and Symptoms
The initial clinical assessment of a person who is
being evaluated for VWD should focus on a personal history of excessive
bleeding throughout the person’s life and any family history of a
bleeding disorder. The history of bleeding should identify the spontaneity and
severity, sites of bleeding, duration of bleeding, type of insult or injury
associated with bleeding, ease with which bleeding can be stopped, and
concurrent medicationssuch as aspirin, other nonsteroidal
antiinflammatory drugs (NSAIDs), clopidogrel (Plavix), warfarin, or
heparinat the onset of bleeding. Particularly when an invasive procedure
is anticipated, the person should be asked whether he or she is currently
taking any of these medications and also whether he or she has any history of
liver or kidney disease, blood or bone marrow disease, or high or low platelet
counts. If a history of any of these illnesses is present, further appropriate
evaluation or referral should be undertaken.
Clinical manifestations. The most common
presenting symptoms in persons subsequently diagnosed with VWD are summarized
in Table 7. Symptoms usually involve mucous membranes and
skin sites, and bleeding is of mild to moderate severity (bleeding that does
not require blood transfusions and usually does not require visits to the
physician) for most persons who have VWD, reflecting the predominance of type 1
VWD. However, lifethreatening bleeding (CNS, gastrointestinal) can occur
in persons who have type 3 VWD, in some persons who have type 2 VWD, and rarely
in persons who have type 1 VWD. Uncommon bleeding manifestations, such as
hemarthrosis, are more common in persons who have a more severe deficiency,
especially those who have type 3 VWD.85,136
Clinical symptoms may also be modified by coexisting illnesses or other
medications. For example, use of aspirin or other NSAIDs can exacerbate the
bleeding tendency, whereas use of oral contraceptives can decrease bleeding in
women who have VWD.
The clinical evaluation of bleeding symptoms is a
challenge, because mild bleeding symptoms are also very common in healthy
populations (Table 7, shaded column). Responses to
questionnaires used to survey healthy controls indicate that they identify
themselves as having specific bleeding manifestations as frequently as persons
who have VWD, particularly type 1 VWD (Table 7).137,138,140,143 In addition, a family history of
bleeding was reported by 44 percent of healthy children undergoing
tonsillectomy143 and by 35
percent138 or 60 percent144 of persons referred because of
bleeding. Because bleeding symptoms are so prevalent, it may be impossible to
establish a causal relationship between bleeding and low VWF.
Figure 3. Initial Evaluation
For VWD or Other Bleeding Disorders
Initial evaluation
strategy to determine which patients would most benefit from further diagnostic
evaluation for von Willebrand disease (VWD) Left Upper Box: Individuals would
be asked three questions about their personal or family bleeding history which,
if any are positive, would lead to a second set of questions selected for their
sensitivity and specificity for VWD (Box 1, below). Those
patients answering positively to one or more of the second set of questions
would benefit from laboratory evaluation. Right Boxes: Patients presenting with
specific information or a concern about bleeding would be asked the Box 1
questions and the initial 3 questions if not already asked, and would also
undergo laboratory evaluation.
Some of the most important
clinical issues in VWD apply specifically to women, particularly menorrhagia.
Studies of women who have VWD report a high prevalence of menorrhagia (Table 7), although the definition of menorrhagia is not
clearly specified in most of these studies and the diagnostic criteria for VWD
are not uniform. The sensitivity of menorrhagia as a predictor of VWD may be
estimated as 32100 percent. However, menorrhagia is a common symptom,
occurring with a similar frequency in healthy controls and women who have VWD;
therefore, it is not a specific marker for VWD (Table 7).
In a survey of 102 women who had VWD and were registered at hemophilia
treatment centers in the United States, 95 percent reported a history of
menorrhagia, but 61 percent of controls also reported a history of
menorrhagia.145 Studies have
reported a prevalence of VWD of between 520 percent among women who have
menorrhagia.146152
Therefore, the specificity of menorrhagia as a predictor of VWD can be
estimated as 520 percent. Three findings that predict abnormal menstrual
blood loss of >80 mL include:
- Clots greater than approximately 1 inch in
diameter
- Low serum ferritin
- Changing a pad or tampon more than hourly153
Box 1. Suggested Questions for
Screening Persons for a Bleeding Disorder
- Do you have a blood relative who has a bleeding
disorder, such as von Willebrand disease or hemophilia?
- Have you ever had prolonged bleeding from trivial
wounds, lasting more than 15 minutes or recurring spontaneously during the 7
days after the wound?
- Have you ever had heavy, prolonged, or recurrent
bleeding after surgical procedures, such as tonsillectomy?
- Have you ever had bruising, with minimal or no
apparent trauma, especially if you could feel a lump under the bruise?
- Have you ever had a spontaneous nosebleed that
required more than 10 minutes to stop or needed medical attention?
- Have you ever had heavy, prolonged, or recurrent
bleeding after dental extractions that required medical attention?
- Have you ever had blood in your stool, unexplained
by a specific anatomic lesion (such as an ulcer in the stomach, or a polyp in
the colon), that required medical attention?
- Have you ever had anemia requiring treatment or
received blood transfusion?
- For women, have you ever had heavy menses,
characterized by the presence of clots greater than an inch in diameter and/or
changing a pad or tampon more than hourly, or resulting in anemia or low iron
level?
Sources: Dean JA, Blanchette VS, Carcao MD,
Stain AM, Sparling CR, Siekmann J, Turecek PL, Lillicrap D, Rand ML. von
Willebrand disease in a pediatricbased populationcomparison of type
1 diagnostic criteria and use of the PFA100® and a von
Willebrand factor/collagenbinding assay. Thromb Haemost 2000
Sep;(3):401409; Drews CD, Dilley AB, Lally C, Beckman MG, Evatt B.
Screening questions to identify women with von Willebrand disease. J Am Med
Womens Assoc 2002;57(4):217218; and Laffan M, Brown SA, Collins PW,
Cumming AM, Hill FG, Keeling D, Peake IR, Pasi KJ. The diagnosis of von
Willebrand disease: a guideline from the UK Haemophilia Centre Doctors’
Organization. Haemophilia 2004 May;10(3):199217.
Table 7. Common Bleeding
Symptoms of Healthy Individuals and Patients Who Have VWD
Symptoms |
Normals (n =
500;137 n= 341;138 n = 88;139 n= 60140) % |
All types VWD (n = 264;137 n = 1,885141) % |
Type 1 VWD (n = 42;142 n = 671136) % |
Type 2 VWD (n = 497136) % |
Type 3 VWD (n = 66;136 n = 38585) % |
Epistaxis |
4.622.7 |
38.162.5 |
5361 |
63 |
6677 |
Menorrhagia* |
2368.4 |
4760 |
32 |
32 |
5669 |
Bleeding after dental extraction |
4.841.9 |
28.651.5 |
1731 |
39 |
5370 |
Ecchymoses |
11.850 |
49.250.4 |
50 |
N.R. |
N.R. |
Bleeding from minor cuts or
abrasions |
0.233.3 |
36 |
36 |
40 |
50 |
Gingival bleeding |
7.447.1 |
26.134.8 |
2931 |
35 |
56 |
Postoperative bleeding |
1.428.2 |
19.528 |
2047 |
23 |
41 |
Hemarthrosis |
014.9 |
6.38.3 |
23 |
4 |
3745 |
Gastrointestinal bleeding |
0.627.7 |
14 |
5 |
8 |
20 |
* Calculated for females above 13 to 15 years of
age. 341 individuals were sent a questionnaire, but the precise
number of patients responding was not provided. Study included
women only. Study included males only. N.R., Not reported.
Identification of people who may require further
evaluation for inherited bleeding disorders. Since other "bleeding
symptoms" besides menorrhagia are reported frequently by persons who have
apparently normal hemostasis, it is important to use questions that can best
identify persons who have a true bleeding disorder. Sramek and
colleagues138 used a written
questionnaire with patients who had a proven bleeding disorder. When the
responses were compared to those of a group of healthy volunteers, the most
informative questions were related to: (1) prolonged bleeding after surgery,
including after dental extractions, and (2) identification of family members
who have an established bleeding disorder (Table 8,
columns 25). A history of muscle or joint bleeding may also be helpful
when associated with the above symptoms.
General questions that relate to isolated bleeding
symptomssuch as frequent gingival bleeding, profuse menstrual blood loss,
bleeding after delivery, and epistaxis in the absence of other bleeding
symptomswere not informative.138 The study also found that an
elaborate interview after referral to a hematologist was not particularly
helpful when attempting to distinguish persons who have a true bleeding
disorder from persons who have a "suspected" bleeding disorder, implying that
the selection of those with bleeding disorders had already been made by the
referring physician.138
Drews et al.139 attempted to develop a
questionnairebased screening tool to identify women who might benefit from a
diagnostic workup for VWD. They conducted a telephone survey of 102 women who
had a diagnosis of type 1 VWD and were treated at a hemophilia treatment center
compared with 88 friends who were controls. With the exception of postpartum
transfusions, all study variables were reported more frequently by women who
had VWD than by their friends (Table 8, columns 6 and 7).
In addition, positive responses to multiple questions were more likely to be
obtained from patients who have an inherited bleeding disorder.139 An important limitation of this study
is that these women were more symptomatic than most women diagnosed as having
type 1 VWD, indicating a more severe phenotype of the disease; this fact might
decrease the sensitivity of the questions in the setting of persons who have
milder type 1 VWD and fewer symptoms.
More recently, Rodeghiero and colleagues155 compared responses to a standardized
questionnaire obtained from 42 obligatory carriers of VWD (from
wellcharacterized families) to responses from 215 controls. The
questionnaire covered 10 common bleeding symptoms (including all symptoms in
Table 7, and postpartum hemorrhage), with assigned scores for each ranging from
0 (no symptoms) to 3 (severe symptoms, usually including hospitalization and/or
transfusion support). With this instrument, the researchers found that having a
cumulative total bleeding score of 3 in men, or 5 in women, was very specific
(98.6 percent) but not as sensitive (69.1 percent) for type 1 VWD. Limitations
of this study include that it was retrospective and that the person
administering the questionnaire was aware of the respondent’s diagnosis.
This questionnaire is available online.155
A similar retrospective casecontrol study154 used a standardized questionnaire
like that of Rodegherio et al.155
to assess bleeding symptoms of 144 index cases who had type 1 VWD, compared to
273 affected relatives, 295 unaffected relatives, and 195 healthy controls. The
interviewers were not blinded to subject’s status. At least one bleeding
symptom was reported by approximately 98 percent of index cases, 89 percent of
affected relatives, 32 percent of unaffected relatives, and 12 percent of
healthy controls. The major symptoms of affected persons (excluding index
cases) included bleeding after tooth extraction, nosebleeds, menorrhagia,
bleeding into the skin, postoperative bleeding, and bleeding from minor wounds.
Using a bleeding score calculated from the data for comparison, the severity of
bleeding diminished with increasing plasma VWF, not only for subjects who had
low VWF levels but throughout the normal range as well. Although the mean
bleeding score was significantly different between several groups, the
distribution was sufficiently broad that the bleeding score could not predict
the affected or unaffected status of individuals.
Table 8. Prevalences of
Characteristics in Patients Who Have Diagnosed Bleeding Disorders Versus
Healthy Controls
Symptom |
Univariate analysis* |
Multivariate analysis* |
Women who
have VWD |
Type 1 VWD
families |
Odds
ratio |
95% CI |
Odds ratio |
95% CI |
Sensitivity |
95% CI |
Odds ratio |
95% CI |
Family members have an established bleeding disorder |
97.5 |
38.3248 |
50.5 |
12.5202.9 |
|
|
|
|
Profuse bleeding from small wounds |
67.2 |
28.4159 |
30.0 |
8.1111.1 |
|
|
16.7 |
2.0137.7 |
Profuse bleeding at site of tonsillectomy/adenoidectomy |
27.7 |
8.096.1 |
11.5 |
1.2111.9 |
|
|
|
|
Easy bruising |
12.7 |
8.020.2 |
9.9 |
3.032.3 |
9.8 |
4.817.3 |
8.1 |
2.130.5 |
Profuse bleeding after surgery |
23.0 |
10.650.1 |
5.8 |
1.326.4 |
52.9 |
42.862.9 |
8.9 |
3.621.8 |
Muscle bleeding (ever) |
13.3 |
6.427.7 |
4.8 |
0.731.4 |
9.8 |
4.817.3 |
|
|
Frequent nosebleeds |
3.5 |
2.06.2 |
3.8 |
0.915.7 |
61.8 |
51.671.2 |
4.9 |
2.410.0 |
Profuse bleeding at site of dental extraction |
39.4 |
20.675.5 |
3.2 |
0.911.3 |
54.9 |
44.764.8 |
4.6 |
2.58.4 |
Blood in stool (ever) |
2.8 |
1.74.6 |
2.8 |
0.711.7 |
13.7 |
7.722.0 |
1.6 |
0.64.3 |
Family members with bleeding symptoms |
28.6 |
15.054.6 |
2.5 |
0.79.4 |
|
|
|
|
Joint bleeding (ever) |
8.6 |
4.815.2 |
2.5 |
0.610.2 |
20.6 |
13.229.7 |
|
|
Menorrhagia |
5.4 |
3.09.8 |
2.5 |
0.69.9 |
|
|
5.1 |
2.610.1 |
Hemorrhage at time of delivery |
5.3 |
2.312.0 |
2.1 |
0.313.5 |
50.0 |
39.960.1 |
0.9 |
0.33.2 |
Frequent gingival bleeding |
2.8 |
1.94.2 |
0.7 |
0.32.0 |
76.5 |
67.084.3 |
1.3 |
0.36.7 |
Hematuria (ever) |
3.2 |
1.85.6 |
0.5 |
0.12.3 |
|
|
|
|
Sources: Sramek A, Eikenboom JC, Briet E,
Vandenbroucke JP, Rosendaal FR. Usefulness of patient interview in bleeding
disorders. Arch Intern Med 1995 Jul;155(13):14091415; Drews CD,
Dilley AB, Lally C, Beckman MG, Evatt B. Screening questions to identify women
with von Willebrand disease. J Am Med Womens Assoc
2002;57(4):217218; and Tosetto A, Rodeghiero F, Castaman G, Goodeve A,
Federici AB, Batlle J, Meyer D, Fressinaud E, Mazurier C, Goudemand J, et al. A
quantitative analysis of bleeding symptoms in type 1 von Willebrand disease:
results from a multicenter European study (MCMDM1 VWD). J Thrombos
Haemostas 2006;4:766773. * Univariate and multivariate analyses
from reference comparing 222 patients who had a known bleeding disorder (43
percent mild VWD) to 341 healthy volunteers.138 Compiled from responses to
a questionnaire sent to 102 women, who had type 1 VWD, in a hemophilia
treatment center.139
Compiled from interviews comparing affected vs. unaffected family members of
patients who have type 1 VWD. The index cases (patients who have VWD) were not
included in the analysis (Tosetto et al. 2006, and personal communication from
Dr. Francesco Rodeghiero on behalf of coauthors).154 CI, confidence interval
In a related study, bleeding symptoms were assessed
with the same questionnaire in 70 persons who were obligatory carriers of type
3 VWD, 42 persons who were obligate carriers of type 1 VWD (meaning affected
family members of index cases who had type 1 VWD), and 215 persons who were
healthy controls.156 Carriers of
type 3 VWD were compared with carriers of type 1 VWD to address the question of
whether the distinct types of VWF mutations associated with these conditions
predisposed to the same or different severity of bleeding. Approximately 40
percent of carriers of type 3 VWD, 82 percent of carriers of type 1 VWD, and 23
percent of healthy controls had at least one bleeding symptom. The major
bleeding symptoms in carriers of type 3 VWD were bleeding into skin and
postsurgical bleeding. The results suggest that carriers of type 3 VWD are
somewhat distinct, as they have bleeding symptoms more frequently than healthy
controls but less frequently than persons who have or are carriers of type 1
VWD. Usually, carriers of type 1 VWD have lower VWF levels than carriers of
type 3 VWD.
Family history. Although a family history
that is positive for an established bleeding disorder is useful in identifying
persons who are likely to have VWD, such a history is frequently not present.
This is most commonly the case for persons who have milder forms of VWD and
whose family members may have minimal, if any, symptoms. As shown in
Table 8, the presence of a documented bleeding disorder
in a family member is extremely helpful in deciding which persons to evaluate
further, whereas a family history of bleeding symptoms is less helpful.
Box 1 summarizes suggested
questions that can be used to identify persons who should be considered for
further evaluation for VWD with laboratory studies.
Physical examination. The physical
examination should be directed to confirm evidence for a bleeding disorder,
including size, location, and distribution of ecchymoses (e.g., truncal),
hematomas, petechiae, and other evidence of recent bleeding. The examination
should also focus on findings that may suggest other causes of increased
bleeding, such as evidence of liver disease (e.g., jaundice), splenomegaly,
arthropathy, joint and skin laxity (e.g., EhlersDanlos Syndrome),
telangiectasia (e.g., hereditary hemorraghic telangiectasia), signs of anemia,
or anatomic lesions on gynecologic examination.
Acquired von Willebrand Syndrome (AVWS).
Persons who have AVWS present with bleeding symptoms similar to those
described, except that the past personal and family history are negative for
bleeding symptoms. AVWS may occur spontaneously or in association with other
diseases, such as monoclonal gammopathies, other plasma cell dyscrasias,
lymphoproliferative diseases, myeloproliferative disorders (e.g., essential
thrombocythemia), autoimmune disorders, valvular and congenital heart disease,
certain tumors, and hypothyroidism.117,157 The evaluation should be tailored to
finding conditions associated with AVWS.
Laboratory Diagnosis and Monitoring
An algorithm for using clinical laboratory studies to
make the diagnosis of VWD is summarized in Figure
4.
Ideally, a simple, single laboratory test could screen
for the presence of VWD. Such a screening test would need to be sensitive to
the presence of most types of VWD and would have a low falsepositive
rate. Unfortunately, no such test is available. In the past, the activated
partial thromboplastin time (PTT) and bleeding time (BT) were recommended as
diagnostic tests. These tests were probably satisfactory for detecting severe
type 3 VWD, but as variant VWD and milder forms of VWD were characterized, it
became apparent that many of the persons who have these conditions had normal
PTT and normal BT results.
An initial hemostasis laboratory evaluation (see Box
2) usually includes a platelet count and complete blood count (CBC), PTT,
prothrombin time (PT), and optionally either a fibrinogen level or a thrombin
time (TT). This testing neither "rules in" nor "rules out" VWD, but it can
suggest whether coagulation factor deficiency or thrombocytopenia might be the
potential cause of clinical bleeding. If the mucocutaneous bleeding history is
strong, consider performing initial VWD assays (VWF:Ag, VWF:RCo, and FVIII) at
the first visit.
Box 2. Initial Laboratory
Evaluation of Hemostasis
- CBC and platelet count
- PTT
- PT
- Fibrinogen or TT (optional)
Figure 4. Laboratory Assessment
For VWD or Other Bleeding Disorders
* Isolated decreased
platelets may occur in VWD type 2B. Correction in the PTT mixing
study immediately and after 2hour incubation removes a factor VIII
(FVIII) inhibitor from consideration. Investigation of other intrinsic
factors and lupus anticoagulant also may be indicated. CBC, complete blood
count; PT prothrombin time; PTT partial thromboplastin time; RIPA,
ristocetininduced platelet aggregation; TT, thrombin time; VWF:Ag, VWF
antigen; VWF:RCo, VWF ristocetin cofactor activity. If the initial
clinical evaluation suggests a bleeding disorder, the "initial hemostasis
tests" should be ordered, followed by or along with the next tests ("initial
VWD assays") indicated in the algorithm. Referral to a hemostasis specialist is
appropriate for help in interpretation, repeat testing, and specialized tests.
Some centers add a BT or a
platelet function analyzer (PFA100®) assay to their
initial laboratory tests. The BT test is a nonspecific test and is fraught with
operational variation. It has been argued that it was a populationbased
test that was never developed to test individuals.158 Variables that may affect results
include a crying or wiggling child, differences in the application of the blood
pressure cuff, and the location, direction, and depth of the cut made by the
device.
This test also has a potential for causing keloid
formation and scarring, particularly in nonCaucasian individuals. The
PFA100® result has been demonstrated to be abnormal in the
majority of persons who have VWD, other than those who have type 2N, but its
use for population screening for VWD has not been established.159162 Persons who have severe type
1 VWD or who have type 3 VWD usually have abnormal PFA100®
values, whereas persons who have mild or moderate type 1 VWD and some who have
type 2 VWD may not have abnormal results.163165 When persons are studied by
using both the BT and PFA100®, the results are not always
concordant.162,164,166
When using the PTT in the diagnosis of VWD, results of
this test are abnormal only if the FVIII is sufficiently reduced. Because the
FVIII gene is normal in VWD, the FVIII deficiency is secondary to the
deficiency of VWF, its carrier protein. In normal individuals, the levels of
FVIII and VWF:RCo are approximately equal, with both averaging 100 IU/dL. In
type 3 VWD, the plasma FVIII level is usually less than 10 IU/dL and represents
the steady state of FVIII in the absence of its carrier protein. In persons who
have type 1 VWD, the FVIII level is often slightly higher than the VWF level
and may fall within the normal range. In persons who have type 2 VWD (except
for type 2N VWD in which it is decreased), the FVIII is often 23 times
higher than the VWF activity (VWF:RCo).167,168 Therefore, the PTT is often
within the normal range. If VWF clearance is the cause of low VWF, the FVIII
reduction parallels that of VWF, probably because both proteins are cleared
together as a complex.
Initial Tests for VWD
Box 3 lists the initial tests commonly used to detect
VWD or low VWF. These three tests, readily available in most larger hospitals,
measure the amount of VWF protein present in plasma (VWF:Ag), the function of
the VWF protein that is present as ristocetin cofactor activity (VWF:RCo), and
the ability of the VWF to serve as the carrier protein to maintain normal FVIII
survival, respectively. If any of the above tests is abnormally low, the next
steps should be discussed with a coagulation specialist, who may recommend
referral to a specialized center, and/or repeating the laboratory tests plus
performing additional tests.
VWF:Ag is an immunoassay that measures the
concentration of VWF protein in plasma. Commonly used methods are based on
enzymelinked immunosorbent assay (ELISA) or automated latex immunoassay
(LIA). As discussed below, the standard reference plasma is critical and should
be referenced to the World Health Organization (WHO) standard. The
person’s test results should be reported in international units (IU),
either as international units per deciliter (IU/dL) or as international units
per milliliter (IU/mL). Most laboratories choose IU/dL, because it is similar
to the conventional manner of reporting clotting factor assays as a percentage
of normal.
VWF:RCo is a functional assay of VWF that
measures its ability to interact with normal platelets. The antibiotic,
ristocetin, causes VWF to bind to platelets, resulting in platelet clumps and
their removal from the circulation. Ristocetin was removed from clinical trials
because it caused thrombocytopenia. This interaction was developed into a
laboratory test that is still the most widely accepted functional test for VWF.
(In vivo, however, it is the high shear in the microcirculation, and not a
ristocetinlike molecule, that causes the structural changes in VWF that
lead to VWF binding to platelets.)
Box 3. Initial Tests for VWD
Several methods are used to assess the platelet
agglutination and aggregation that result from the binding of VWF to platelet
GPIb induced by ristocetin (ristocetin cofactor activity, or VWF:RCo). The
methods include: (1) time to visible platelet clumping using ristocetin, washed
normal platelets (fresh or formalinized), and dilutions of patient plasma; (2)
slope of aggregation during platelet aggregometry using ristocetin, washed
normal platelets, and dilutions of the person’s plasma; (3) automated
turbidometric tests that detect platelet clumping, using the same reagents
noted above; (4) ELISA assays that assess direct binding of the person’s
plasma VWF to platelet GPIb (the GPIb may be derived from plasma glycocalicin)
in the presence of ristocetin;169171 and (5) the binding of a
monoclonal antibody to a conformation epitope of the VWF A1 loop.172 Method 5 can be performed in an ELISA
format or in an automated latex immunoassay. It is not based on ristocetin
binding. The first three assays (above) may use platelet membrane fragments
containing GPIb rather than whole platelets. The sensitivity varies for each
laboratory and each assay; in general, however, Methods 1 and 2, which measure
platelet clumping by using several dilutions of the person’s plasma, are
quantitative to approximately 612 IU/dL levels. Method 3 is quantitative
to about 1020 IU/dL. Method 4 can measure VWF:RCo to <1 IU/dL, and a
variation of it can detect the increased VWF binding to GPIb seen in type 2B
VWD.173 Some automated methods
are less sensitive and require modification of the assay to detect <10
IU/dL. Each laboratory should define the linearity and limits of its assay.
Several monoclonal ELISAs (Method 5) that use antibodies directed to the VWF
epitope containing the GPIb binding site have been debated because the
increased function of the largest VWF multimers is not directly
assessed.174
The ristocetin cofactor activity (VWF:RCo) assay has
high intra and interlaboratory variation, and it does not actually
measure physiologic function. The coefficient of variation (CV) has been
measured in laboratory surveys at 30 percent or greater, and the CV is still
higher when the VWF:RCo is lower than 1215 IU/dL.175179 This becomes important not
only for the initial diagnosis of VWD, but also for determining whether the
patient has type 1 versus type 2 VWD (see discussion on VWF:RCo to VWF:Ag
ratio, below). Despite these limitations, it is still the most widely accepted
laboratory measure of VWF function. Results for VWF:RCo should be expressed in
international units per deciliter (IU/dL) based on the WHO plasma standard.
FVIII coagulant assay is a measure of the
cofactor function of the clotting factor, FVIII, in plasma. In the context of
VWD, FVIII activity measures the ability of VWF to bind and maintain the level
of FVIII in the circulation. In the United States, the assay is usually
performed as a onestage clotting assay based on the PTT, although some
laboratories use a chromogenic assay. The clotting assay, commonly done using
an automated or semiautomated instrument, measures the ability of plasma FVIII
to shorten the clotting time of FVIIIdeficient plasma. Because this test
is important in the diagnosis of hemophilia, the efforts to standardize this
assay have been greater than for other hemostasis assays. FVIII activity is
labile, with the potential for spuriously low assay results if blood specimen
collection, transport, or processing is suboptimal. Like those tests discussed
above, it should be expressed in international units per deciliter (IU/dL)
based on the WHO plasma standard.
Expected patterns of laboratory results in
different subtypes of VWD, depicted in Figure 5,
include results of the three initial VWD tests (VWF:Ag, VWF:RCo, FVIII) and
results of other assays for defining and classifying VWD subtypes. The three
initial tests (or at least the VWF:RCo and FVIII assays) are also used for
monitoring therapy.
Other Assays To Measure VWF, Define/Diagnose VWD, and
Classify Subtypes
The VWF multimer test, an assay that is
available in some larger centers and in commercial laboratories, is usually
performed after the initial VWD testing indicates an abnormality, preferably
using a previously unthawed portion of the same sample or in association with a
repeated VWD test panel (VWF:Ag, VWF:RCo, FVIII) using a fresh plasma sample.
VWF multimer analysis is a qualitative assay that depicts the variable
concentrations of the differentsized VWF multimers by using sodium
dodecyl sulfate (SDS)protein electrophoresis followed by detection of the
VWF multimers in the gel, using a radiolabeled polyclonal antibody or a
combination of monoclonal antibodies. Alternatively, the protein is transferred
to a membrane (Western blot), and the multimers are identified by
immunofluorescence or other staining techniques.99,180,181
Figure 5. Expected Laboratory
Values in VWD
The symbols and values represent
prototypical cases. In practice, laboratory studies in certain patients may
deviate slightly from these expectations. L, 3050 IU/dL; ↓,
↓↓, ↓↓↓, relative decrease; ↑, ↑↑,
↑↑↑, relative increase; BT, bleeding time; FVIII, factor VIII
activity; LDRIPA, lowdose ristocetininduced platelet
aggregation (concentration of ristocetin ≤ 0.6 mg/mL); N, normal;
PFA100® CT, platelet function analyzer closure time; RIPA,
ristocetininduced platelet aggregation; VWF, von Willebrand factor;
VWF:Ag, VWF antigen; VWF:RCo, VWF ristocetin cofactor activity. *Note:
persons who have platelettype VWD (PLTVWD) have a defect in their
platelet GPIb. Laboratory test results resemble type 2B VWD, and both have a
defect in their LDRIPA. In the VWF:platelet binding assay (see text),
persons who have type 2B VWD have abnormally increased platelet binding. Normal
persons and those who have PLTVWD have no binding of their VWF to normal
platelets at low ristocetin concentrations. Note: this figure is
adapted from and used by permission of R.R. Montgomery.
Multimer assays are designated as "low resolution"
(which differentiate the largest multimers from the intermediate and small
multimers) or "high resolution" (which differentiate each multimer band of the
smaller multimers into three to eight satellite bands). For diagnostic
purposes, the lowresolution gel systems are used primarily; these systems
help to differentiate the type 2 VWD variants from types 1 or 3 VWD.
Figure 6 illustrates the differences between these two
techniques with regard to the resolution of high and
lowmolecularweight multimers. It should be noted that multimer
appearance alone does not define the variant subtype and that only types 2A,
2B, and platelettype VWD (PLTVWD) have abnormal multimer
distributions with relative deficiency of the largest multimers. An exception
is Vicenza variant VWD with ultralarge VWF multimers and low VWF. For more
information about VWF multimer findings in type 2 VWD variants, see
descriptions above (type 2 VWD)
and associated references.
LowDose RIPA. RIPA and VWF
plateletbinding assay (VWF:PB assay) are two tests that are performed to
aid in diagnosing type 2B VWD. RIPA may be done as part of routine platelet
aggregation testing. RIPA is carried out in plateletrich plasma, using a
low concentration of ristocetin (usually <0.6 mg/mL, although ristocetin
lots vary, resulting in the use of slightly different ristocetin
concentrations). This low concentration of ristocetin does not cause VWF
binding and aggregation of platelets in samples from normal persons, but it
does cause VWF binding and aggregation of platelets in samples from patients
who have either type 2B VWD or mutations in the platelet VWF receptor. The
latter defects have been termed platelettype (PLTVWD) or pseudo
VWD, and they can be differentiated from type 2B VWD by VWF:PB assay. At higher
concentrations of ristocetin (1.11.3 mg/mL), RIPA will be reduced in
persons who have type 3 VWD. However, the test is not sufficiently sensitive to
reliably diagnose other types of VWD.
Figure 6. Analysis of VWF
Multimers
The distribution of VWF multimers can
be analyzed using sodium dodecyl sulfate (SDS)agarose electrophoresis
followed by immunostaining. Lowresolution gels (0.65% agarose, left side)
can demonstrate the change in multimer distribution of the larger multimers
(top of the gel), while highresolution gels (23% agarose, right
side) can separate each multimer into several bands that may be distinctive.
For example, the lowest band in the 0.65% gel (1) can be resolved into 5 bands
in the 3% agarose gel, but the 3% gel fails to demonstrate the loss of high
molecular weight multimers seen at the top in the 0.65% gel. The dotted lines
(1) indicate the resolution of the smallest band into several bands in the 3%
agarose gel. In each gel, normal plasma (NP) is run as a control. Type 1 VWD
plasma has all sizes of multimers, but they are reduced in concentration. Type
2A VWD plasma is missing the largest and intermediate multimers, while type 2B
VWD plasma is usually missing just the largest VWF multimers. No multimers are
identified in type 3 VWD plasma. Patients who have thrombotic thrombocytopenic
purpura (TTP) may have larger than normal multimers when studied with
lowresolution gels. Note: Used by permission of R.R. Montgomery.
VWF: plateletbinding (VWF:PB) assay
measures the binding of VWF to normal paraformaldehydefixed platelets
using low concentrations of ristocetin (usually 0.30.6 mg/mL).182 The amount of VWF bound to the fixed
platelets is determined by using a labeled antibody. Normal individuals, or
those who have types 1, 2A, 2M, 2N, and 3 VWD, exhibit minimal or no binding to
platelets at the concentration of ristocetin used, but patients who have type
2B VWD exhibit significant binding that causes their variant phenotype (a loss
of highmolecularweight multimers, decreased ristocetin cofactor
activity, and thrombocytopenia). Both type 2B VWD and platelettype VWD
have agglutination of plateletrich plasma (PRP) to lowdose
ristocetin, but the VWF:PB assay can differentiate type 2B VWD from
platelettype VWD. Only VWF from persons who have type 2B VWD has increased
VWF:PB, while VWF from persons who have platelettype VWD has normal
VWF:PB with low doses of ristocetin.
VWF collagenbinding (VWF:CB) assay
measures binding of VWF to collagen. The primary site of fibrillar collagen
binding is in the A3 domain of VWF. Like the ristocetin cofactor assay, the
collagen binding assay is dependent on VWF multimeric size, with the largest
multimers binding more avidly than the smaller forms. The VWF:CB assay
performance and sensitivity to VWD detection or discrimination among VWD
subtypes is highly dependent on the source of collagen, as well as on whether
type 1 collagen or a mixture of type 1/3 collagen is used.183,184 Only a few patients have been
identified who have specific collagenbinding defects that are independent
of multimer size, and the defects have been associated with a mutation of VWF
in the A3 domain.73 The prevalence
of such defects is unknown. The place of VWF:CB in the evaluation of VWD has
not been established. In principle, however, patients who have defects in
collagen binding may have a normal VWF:RCo and thus escape clinical diagnosis
unless a VWF:CB assay is performed. Limited studies suggest that supplementary
VWF:CB testing, complementing assays of VWF:RCo and VWF:Ag, can improve the
differentiation of type 1 VWD from types 2A, 2B, or 2M VWD.175,185,186
VWF:FVIII binding (VWF:FVIIIB) assay measures
the ability of a person’s VWF to bind added exogenous FVIII and is used
to diagnose type 2N VWD.75,77,78,187,188 The assay is performed by
capturing the person’s VWF on an ELISA plate, removing the bound
endogenous FVIII, and then adding back a defined concentration of exogenous
recombinant FVIII. The amount of FVIII bound is determined by a chromogenic
FVIII assay. The level of this bound FVIII is then related to the amount of the
person’s VWF initially bound in the same well. In clinical experience,
Type 2N VWD is usually recessive; the person is either homozygous or compound
heterozygous (one allele is type 2N, and the other is a type 1 or "null"
allele). In either case, the VWF in the circulation does not bind FVIII
normally, and the concentration of FVIII is thus decreased.
The VWF:RCo to VWF:Ag ratio can aid in the
diagnosis of types 2A, 2B, and 2M VWD and help differentiate them from type 1
VWD. For example, VWF:RCo/VWF:Ag <0.6189 or <0.7 has been used as a
criterion for dysfunctional VWF.8,190 A
similar approach has been proposed for the use of the VWF:CB/VWF:Ag
ratio.8,190 In type 2A VWD, the ratio is usually
low; and in type 2B VWD, the VWF:RCo/VWF:Ag ratio is usually low but may be
normal. In type 2M VWD, the VWF:Ag concentration may be reduced or normal, but
the VWF:RCo/VWF:Ag ratio will be <0.7. One study70 determined the VWF:RCo/VWF:Ag ratio in
nearly 600 individuals with VWF levels <55 IU/dL who had normal VWF
multimers. The study used this ratio to identify families who had type 2 VWD,
but most centers do not have the ability to establish normal ranges for
patients who have low VWF. Additionally, the VWF:RCo assay has a coefficient of
variation (CV) as high as 30 percent or more, depending on methodology, whereas
the CV for the VWF:Ag assay is somewhat lower. The high intrinsic variability
of the VWF:RCo assay, especially at low levels of VWF, can make the
VWF:RCo/VWF:Ag ratio an unreliable criterion for the diagnosis of type 2
VWD.175,177179 (See Recommendations
II.C.1.a. and III.B.1, below). It is important that the same plasma standard be
used in both the VWF:RCo and VWF:Ag assays and that the normal range for the
VWF:RCo/VWF:Ag ratio and its sensitivity to types 2A and 2M VWD be determined
in each laboratory. Because no large multicenter studies have evaluated the
precise ratio that should be considered abnormal, a ratio in the range of less
than 0.50.7 should raise the suspicion of types 2A, 2B, or 2M VWD.
Further confirmation should be sought by additional testing (e.g., repeat VWD
test panel and VWF multimer study or sequencing of the A1 region of the VWF
gene).191
ABO blood types have a significant effect on
plasma VWF (and FVIII) concentrations.43,192
Individuals who have blood type O have concentrations approximately 25 percent
lower compared to persons who have other ABO blood types. The diagnosis of type
1 VWD occurs more frequently in individuals who have blood group type O.43 Table 9
illustrates the significant effect of blood type on VWF:Ag level.
Table 9. Influence of ABO Blood Groups on VWF:Ag
ABO Type |
N |
VWF:Ag mean |
Range |
O |
456 |
74.8* |
35.6157.0*
(41179) |
A |
340 |
105.9* |
48.0233.9*
(55267) |
B |
196 |
116.9* |
56.8241.0*
(65275) |
AB |
109 |
123.3* |
63.8238.2*
(73271) |
*U/dL; IU/dL Source: Gill
JC, EndresBrooks J, Bauer PJ, Marks WJ, Jr., Montgomery RR. The effect of
ABO blood group on the diagnosis of von Willebrand disease. Blood 1987
Jun;69(6):16911695. Copyright American Society of Hematology, used with
permission. In this publication, VWF:Ag was expressed as U/dL, but the range in
IU/dL (WHO) is higher for all blood groups, as noted in the values in
parentheses (personal communication from R.R. Montgomery, J.L. Endres, and K.D.
Friedman).
Although it has been recommended to stratify reference
ranges for VWF:Ag and VWF:RCo with respect to blood group O and nongroup
O,193,194 evolving limited
information supports the concept that, despite the ABO blood grouping and
associated VWF reference ranges, the major determinant of bleeding symptoms or
risk is low VWF.189,195,196 Therefore, referencing VWF
testing results to the population reference range, rather than to
ABOstratified reference ranges, may be more useful clinically.
Platelet VWF studies are performed by some
laboratories, including VWF:RCo, VWF:Ag, and VWF multimers, using VWF extracted
from washed platelets. The methods and interpretations of these studies,
however, are not well standardized.
DNA sequencing of patient DNA has been used
to make a molecular diagnosis of variants of type 2 VWD,197199 but DNA sequencing is not
widely available. Most of the mutations found in types 2B, 2M, and 2N VWD
cluster in the cDNA that directs the synthesis of specific regions of VWF (see
Figure 2).200 In the common forms of type 2A VWD,
in which the VWF is spontaneously cleaved by ADAMTS13, mutations cluster in the
A2 domain (which contains the cleavage site). In the less common type 2A
variants of VWD, in which multimer formation is inhibited, the mutations may be
scattered throughout the gene. In most persons who have type 1 VWD, the genetic
mutations have not been established, although several studies are being
conducted at present to characterize these mutations.
Assays for Detecting VWF Antibody
Assays for detecting antiVWF antibodies are not
as well established as the assays for detecting antibodies to FVIII in patients
who have hemophilia A. Some patients who have AVWS do appear to have
antiVWF antibodies that decrease the halflife of infused VWF.
Although a few antibodies do inhibit VWF function and can be demonstrated in
1:1 mixing studies with normal plasma using the VWF:RCo assay, most
antiVWF antibodies are not "inhibitors" of VWF function. The presence of
these antibodies, however, promotes rapid clearance of VWF. The plasma level of
VWF propeptide (VWFpp) is normally proportionate to the level of VWF:Ag, and
the VWFpp level can be measured to aid in the detection of the rapid clearance
of VWF. Accelerated plasma clearance of VWF:Agas occurs in some patients
who have AVWS, in those who have certain type 1 VWD variants, or in those who
have type 3 VWD and have alloantibodies to VWFis associated with an
increase in the ratio of VWFpp to VWF:Ag.201,202 Persons who have type 3 VWD, with
large deletions of the VWF gene, are prone to develop alloantibodies to
transfused VWF.203 Patients who
have AVWS, VWF antibodies, or mutations that affect VWF clearance can be
studied using VWFsurvival testing after administration of DDAVP or VWF
concentrate.
Making the Diagnosis of VWD
Scoring systems and criteria for assessing the
bleeding history and the probability of having VWD, especially type 1 VWD, are
in evolution but have not yet been subjected to prospective studies outside of
defined populations.155,194 Establishing the diagnosis of VWD in
persons who have type 2 VWD variants and type 3 VWD is usually straightforward,
based on the initial VWD tests (described in Box 3 above,
Initial Tests for VWD). Treatment depends on the specific subtype (e.g., type
2A, 2B, 2M, or 2N), which is determined by additional tests including VWF
multimer analysis. In contrast, the diagnosis of type 1 VWD is often more
difficult,21,44,93,114,204 partly because not all persons who
have decreased levels of VWF have a molecular defect in the VWF gene. Whether
individuals who do not have an abnormality in the VWF gene should be diagnosed
as having VWD or should be given another designation is currently under
consideration (see section on "Type
1 VWD Versus Low VWF"). The reasons for reduced VWF levels in many of these
persons who have a normal VWF gene sequence are not understood. A "low" VWF
level is believed to confer some bleeding risk, despite having a normal VWF
gene, and those persons who have clinical bleeding and low VWF may benefit from
treatment to raise the VWF level. Most clinicians would agree that persons
having VWF levels below 30 IU/dL probably have VWD. It is likely that most of
these persons have a mutation in the VWF gene. Currently, several large
European Union, Canadian, and U.S. studies are trying to define that frequency.
Persons whose plasma VWF levels are below the lower limit of the laboratory
reference range, but >30 IU/dL, may have VWD but are sometimes referred to
as having "possible type 1 VWD" or "low VWF." There is no generally accepted
designation for these persons. Although type 3 VWD is usually the result of
inheriting two "null" alleles, the heterozygous "carriers" in these families do
not universally have a significant bleeding history; therefore, type 3 VWD has
been called a recessive disorder.21,44,101
Special Considerations for Laboratory Diagnosis of
VWD
Repeated testing for VWD is sometimes needed to
identify low levels of VWF. Stressincluding surgery, exercise,
anxiety, crying in a frightened child, as well as systemic inflammation,
pregnancy, or administration of estrogen/oral contraceptives can cause an
increase in plasma levels of VWF and mask lower baseline values. VWF levels
vary with the menstrual cycle, and lowest values are detected on days 14
of the menstrual cycle. However, the importance of timing of the testing with
respect to the menstrual cycle is not clear. Family studies may be helpful to
diagnose hereditary decreases in VWF levels.
Problems may occur in preparing samples for
testing. As noted, anxiety may falsely elevate the VWF and FVIII levels,
and the setting for phlebotomy should be as calm as possible. It is important
that the sample be obtained by atraumatic collection of blood, drawn into the
appropriate amount of citrate anticoagulant. The College of American
Pathologists (CAP), as well as the Clinical Laboratory Standards Institute
(CLSI, formerly NCCLS), recommend collecting blood into 3.2 percent citrate,
although some laboratories still use 3.8 percent citrate. Fasting or nonlipemic
samples should be used for testing, and icteric or hemolyzed samples may also
compromise the quality of testing results.193,205 If a person has polycythemia or
profound anemia, the amount of anticoagulant should be adjusted on the basis of
nomograms for this purpose. Blood should be centrifuged promptly to obtain
plasma, and the plasma should remain at room temperature if assays are to be
completed within 2 hours. Whole blood should not be transported on wet ice (or
frozen).206,207 If plasma samples
are frozen, they should be thawed at 37°C to avoid formation of a
cryoprecipitate. Plasma assays should be performed on "plateletpoor" or
"plateletfree" plasma.193
Although a small number of platelets may not significantly affect studies done
on fresh plasma, freezing these samples may result in the release of proteases
or platelet membrane particles that affect plasma assays for VWF. Thus, plasmas
should be centrifuged carefully. Some laboratories perform double
centrifugation to ensure platelet removal. The integrity of samples may suffer
during transport to an outside laboratory, and steps should be taken that can
best ensure prompt delivery of frozen samples. (See Table
10, below.)
The VWF reference standard is critical to the
laboratory diagnosis of VWD. When possible, all laboratory assays of VWF
should use the same standard to avoid artifactual discrepancies. Results of VWF
assays can be reported in international units (IUs) only if they have been
referenced to the WHO standard for that analyte. If a reference plasma pool is
used, it is usually reported as a percentage of normal, as it cannot be called
an IU. To assist the comparison, IUs are usually expressed as IU/dL so that the
reported values have the same range as "percentage of normal plasma"
values.
Table 10. Collection and
Handling of Plasma Samples for Laboratory Testing
Phlebotomy conditionsAn
atraumatic blood draw limits the exposure of tissue factor from the site and
the activation of clotting factors, minimizing falsely high or low values.
Patient stress levelUndue
stress, such as struggling or crying in children or anxiety in adults, may
falsely elevate VWF and FVIII levels. Very recent exercise can also elevate VWF
levels.
Additional conditions in the
personThe presence of an acute or chronic inflammatory illness
may elevate VWF and FVIII levels, as may pregnancy or administration of
estrogen/oral contraceptives.
Sample processingTo prevent
cryoprecipitation of VWF and other proteins, blood samples for VWF assays
should be transported to the laboratory at room temperature. Plasma should be
separated from blood cells promptly at room temperature, and the plasma should
be centrifuged thoroughly to remove platelets. If plasma samples will be
assayed within 2 hours, they should be kept at room temperature. Frozen plasma
samples should be carefully thawed at 37°C and kept at room temperature for
<2 hours before assay.
Sample storagePlasma samples
that will be stored or transported to a reference laboratory must be frozen
promptly at or below 40°C and remain frozen until assayed. A control
sample that is drawn, processed, stored, and transported under the same
conditions as the tested person’s sample may be helpful in indicating
problems in the handling of important test samples.
Laboratory variables also occur. The
variability (CV) of the VWF:RCo assay is high (2030 percent or greater)
and the CV of the VWF:Ag assay is also relatively high (1020 percent or
greater), as is the CV for the FVIII assay.175,177179,183,208210 The quality of laboratory
testing also varies considerably among laboratories (high interlaboratory CV).
Coupled with variability of VWF and FVIII contributed by conditions of the
patient and the blood sample, the high variability of these three diagnostic
tests can contribute to difficulty in diagnosing VWD or classifying the VWD
subtype (e.g., type 1 vs. type 2 variant, using the VWF:RCo to VWF:Ag ratio).
Some of the more specialized tests, such as VWF multimer analysis likely also
have high variability of test performance and interpretation,180,181 and they are often not available
at local testing laboratories.
Summary of the Laboratory Diagnosis of VWD
The diagnosis of VWD can be complex, and no single
diagnostic approach is suitable for all patients. Improvements in laboratory
testing and quality, along with further research into the frequency of
mutations of the VWF gene, alterations of other proteins that result in reduced
VWF levels, and the correlation of clinical symptoms with laboratory test
levels will be necessary to place the diagnosis of VWD on a more secure
foundation. (See Table 10, above.)
The following recommendations include specific
clinical history, physical findings, laboratory assays, and diagnostic criteria
that this Panel suggests will allow the most definitive diagnosis of VWD.
- Tests such as the bleeding time,
PFA100®, or other automated functional platelet assays
have been used but there are conflicting data with regard to sensitivity and
specificity for VWD.162,164,166 Therefore, the Panel believes current
evidence does not support their routine use as screening tests for VWD.
- The Panel believes that plateletbased assays
should be used for the ristocetin cofactor method.
- The Panel emphasizes the importance of the timing
of the phlebotomy for assays, with the patient at his/her optimal baseline as
far as possible. (For example, VWF levels may be elevated above baseline during
the second and third trimesters of pregnancy or during estrogen replacement,
during acute inflammation such as the perioperative period, during infections,
and during acute stress.) The careful handling and processing of the sample is
also critical, particularly if the sample will be sent out for testing at a
distant location.
Diagnostic Recommendations
The recommendations are graded according to criteria
described in "Clinical
RecommendationsGrading and Levels of Evidence" and Table 1.
Evidence tables are provided for
recommendations given a grade of B and having two or more references.
- Evaluation
of Bleeding Symptoms and Bleeding Risk by History and Physical Examination
Summarized in Figure 3, and Box 1.
- Ask the following broad questions:
- Have you
or a blood relative ever needed medical attention for a bleeding problem, or
have you been told you had a bleeding problem? Grade B, level IIb138
If the answer is "Yes" to
either of the broad questions above, ask the additional probes:
- Have you needed medical attention for
bleeding? After surgery? After dental work? With trauma?
- Have you ever had bruises so large they
had lumps?
Grade B, level IIb138
- Do you
have or have you ever had:
- Liver or kidney disease?
- A blood or bone marrow disorder?
- A high or low platelet count?
If the
answer is "Yes" to any of these questions, obtain relevant details. Grade
C, level IV
- Are you
currently taking, or have you recently taken anticoagulation or antiplatelet
medications (warfarin, heparin, aspirin, NSAIDs, clopidogrel)?
If the
answer is "Yes", obtain relevant details. Grade C, level IV
- If
answers to questions I.A.1 are positive, ask if the patient or any blood
relatives have had:
- A
bleeding disorder, such as von Willebrand disease or hemophilia?
- Prolonged bleeding, heavy, or recurrent from:
- Trivial wounds, lasting more than 15
minutes or recurring spontaneously during the 7 days after the wound?
- Surgical procedures, such as
tonsillectomy?
- Bruising
with minimal or no apparent trauma, especially if you could feel a lump?
- Spontaneous nosebleeds that required more than
10 minutes to stop or needed medical attention?
- Dental
extractions leading to heavy, prolonged, or recurrent bleeding?
- Blood in
your stool, unexplained by a specific anatomic lesion (such as an ulcer in the
stomach, or a polyp in the colon), that required medical attention?
- Anemia
requiring treatment or received a blood transfusion?
- For
women, heavy menses, characterized by the presence of clots greater than an
inch in size and/or changing a pad or tampon more than hourly, or resulting in
anemia or low iron level?
If answers to above questions I.B.18 are
positive, obtain relevant specific information. Grade B, level IIb138,139
See Evidence Table 1.
- Perform
a physical examination to include evaluation for:
- Evidence for a bleeding disorder,
including size, location, and distribution of ecchymoses (e.g., truncal),
hematomas, petechiae, and other evidence of recent bleeding and/or anemia.
Grade C, level IV
- Evidence
that suggests other causes or risks of increased bleeding, such as jaundice or
spider angiomata (liver disease), splenomegaly, arthropathy, joint and skin
laxity (e.g., EhlersDanlos Syndrome), telangiectasia (e.g., hereditary
hemorraghic telangiectasia), or evidence of anatomic lesions on gynecologic
examination. Grade C, level IV
return to text, after Figure
3
Laboratory testing should be guided by the history
and physical findings (section I.) and the initial laboratory evaluation (see
II.A., below). For example, findings of liver disease may lead to a different
or additional laboratory evaluation rather than an evaluation for VWD (see
II.B., below).
- Evaluation
by Laboratory Testing
- Initial
laboratory evaluation for the etiology of a bleeding disorder should include:
- A
complete blood count (CBC including platelet count), prothrombin time (PT),
activated partial thromboplastin time (PTT), and optionally either thrombin
time or fibrinogen level.
- If
laboratory abnormalities besides the PTT are present (the platelet count may
also be decreased in type 2B VWD), in conjunction with the history and physical
examination findings, consider bleeding disorders other than VWD or additional
underlying diseases.
- If the
mucocutaneous bleeding history is strong, consider performing initial VWD
assays at the first visit (see II.B., below).
- If there
are no abnormalities on initial blood testing, or if there is an isolated
prolonged PTT that corrects on the 1:1 mixing study, the following three tests
for VWD should be performed (II.B., below), unless another cause for bleeding
has been identified and VWD is not likely (see Figure
4). For further laboratory evaluation, physicians may consider referral to
a hemostasis center because of the special sample handling and testing
requirements (see Table 10).
Grade C, level
IV
- Initial
tests for diagnosing or excluding VWD include the following three tests:
- VWF:RCo
- VWF:Ag
- Factor
VIII activity
Grade B, level III3,43,175,176 See Evidence Table 2.
- If any
one of the above test results is abnormally low, a discussion with or a
referral to a hemostasis expert is appropriate. In addition to repeating the
initial three tests (in most cases), the specialist may recommend appropriate
studies from the following:
- The
first set of additional tests may include:
- Evaluation of the ratio of VWF activity
(VWF:RCo and/or VWF:CB) to VWF antigen (only in laboratories that have defined
reference ranges for the ratio[s]) Grade B, level III70,71,91,163,175,190 See Evidence Table 3.
- VWF multimer study
Grade B, level
III181
- Ristocetininduced platelet
aggregation
Grade B, level III46
- VWF collagen binding activity (VWF:CB)
Grade B, level IIb175,185,186 See Evidence Table 4.
- Studies
in selected patients, especially those who have discordantly low FVIII activity
compared to VWF levels and who are suspected of having type 2N VWD, should
include a FVIII binding assay (VWF:FVIIIB) Grade B, level IIb77,78,188 See Evidence Table 5.
- Additional studies in selected persons may
include:
- Gene sequencing
Grade C, level
IV
- Assays for antibodies to VWF
Grade
C, level IV
- Plateletbinding studies
Grade B, level III182
- Making the
Diagnosis
- Clinical criteria.Clinical
criteria. These criteria include personal and/or family history and/or physical
evidence of mucocutaneous bleeding. Until further validation of scoring systems
and criteria for assessing bleeding history and the probability of VWD,
especially type 1 VWD, the Expert Panel suggests that an increasing number of
positive responses to the questions about bleeding (Figure
3, and Box 1) and abnormal findings on physical
examination increase the likelihood that an individual has a bleeding disorder,
including possible VWD.
AND
- Laboratory criteria. The values
in the following table represent prototypical cases without additional VWF (or
other disease) abnormalities in the patient. In practice, exceptions occur, and
repeat testing and clinical experience are important and may be necessary for
interpretation of laboratory results.
- Although
published evidence is limited, for defining the ratio of VWF:RCo/VWF:Ag to use
for distinguishing type 1 VWD versus type 2 VWD variants (A, B, or M), the
Expert Panel recommends a ratio of <.50.7 until more laboratories
clearly define a reference range using large numbers of normal subjects and
persons who have type 1 VWD and type 2 VWD variants.
Grade C, level
IV70,71,91,163,189,190
- The
panel currently recommends that 30 IU/dL be used as the "cutoff" level
for supporting the definite diagnosis of VWD for the following reasons:
- There is a high frequency of blood
type O in the United States, and it is associated with "low" VWF levels;43
- Bleeding symptoms are reported by a
significant proportion of normal individuals;137140 and
- No abnormality in the VWF gene has
been identified in many individuals who have mildly to moderately low VWF:RCo
levels
Grade C, level IV100102
- This recommendation does
not preclude the diagnosis of VWD in individuals with VWF:RCo of 3050
IU/dL if there is supporting clinical and/or family evidence for VWD. This
recommendation also does not preclude the use of agents to increase VWF levels
in those who have VWF:RCo of 3050 IU/dL and may be at risk for
bleeding.
Condition |
VWF:RCo (IU/dL) |
VWF:Ag (IU/dL) |
FVIII |
Ratio of VWF:RCo/ VWF:Ag |
Type 1 |
<30* |
<30* |
↓ or Normal |
>0.50.7 |
Type 2A |
<30* |
<30200* |
↓ or Normal |
<0.50.7 |
Type 2B |
<30* |
<30200* |
↓ or Normal |
Usually <0.50.7 |
Type 2M |
<30* |
<30200* |
↓ or Normal |
<0.50.7 |
Type 2N |
30200 |
30200 |
↓↓ |
>0.50.7 |
Type 3 |
<3 |
<3 |
↓↓↓(<10 IU/dL) |
Not applicable |
"Low VWF" |
3050 |
3050 |
Normal |
>0.50.7 |
Normal |
50200 |
50200 |
Normal |
>0.50.7 |
↓ refers to a decrease in the test result
compared to the laboratory reference range. * <IU/dL is designated as
the level for a definitive diagnosis of VWD; there are some patients with type
1 or type 2 VWD who have levels of VWF:RCo and/or VWF:Ag of 3050 IU/dL.
The VWF:Ag in the majority of individuals with type 2A,
2B, or 2M VWD is <50 IU/dL.
return to text, after Figure
4
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