Were you looking for the high-sensitivity CRP (hs-CRP) test, used to assess your risk of cardiovascular disease?
At a Glance
Why Get Tested?
To identify the presence of inflammation and to monitor response to treatment for an inflammatory disorder
When to Get Tested?
When your doctor suspects that you have an acute condition causing inflammation, such as a serious bacterial or fungal infection or when you are suffering from an inflammatory disorder such as arthritis, an autoimmune disorder, or inflammatory bowel disease
Sample Required?
A blood sample taken from a vein in your arm
Test Preparation Needed?
None
The Test Sample
What is being tested?
C-reactive protein (CRP) is an acute phase reactant, a protein made by the liver and released into the bloodstream within a few hours after tissue injury, the start of an infection, or other cause of inflammation. Markedly increased levels are observed, for example, after trauma, heart attack, with autoimmune disorders, and with serious bacterial infections like sepsis. The level of CRP can jump a thousand-fold in response to an inflammatory condition, and its rise in the blood can precede pain, fever, or other clinical indicators. The test measures the amount of CRP in the blood and can be valuable in detecting inflammation due to acute conditions or in monitoring disease activity in chronic conditions.
The CRP test is not diagnostic, but it provides information to the doctor as to whether inflammation is present. This information can be used by the doctor in conjunction with other factors, such as signs and symptoms, physical exam and other tests to determine if someone has an acute inflammatory condition or if they are experiencing a flare-up of a chronic inflammatory disease. The doctor may then follow up with further testing and treatment.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
The Test
How is it used?
C-reactive protein (CRP) is a non-specific test. It is used by a doctor to detect inflammation if there is a high suspicion of tissue injury or infection somewhere in the body, but the test cannot tell where the inflammation is or what condition is causing it. CRP is not diagnostic of any condition, but it can be used together with signs and symptoms and other tests to evaluate an individual for an acute or chronic inflammatory condition.
For example, CRP may be used to detect or monitor significant inflammation in an individual who is suspected of having an acute condition such as:
- A serious bacterial infection like sepsis or a fungal infection
- Pelvic inflammatory disease (PID)
The CRP test is useful in monitoring people with chronic inflammatory conditions to detect flare-ups and/or to determine if treatment is effective. Some examples include:
- Inflammatory bowel disease
- Some forms of arthritis
- Autoimmune diseases, such as lupus or vasculitis
CRP may sometimes be ordered along with an Erythrocyte Sedimentation Rate (ESR), another test that detects inflammation. While the CRP test is not specific enough to diagnose a particular disease, it does serve as a general marker for infection and inflammation, thus alerting medical professionals that further testing and treatment may be necessary. Depending on the suspected cause, a number of other tests may be performed to identify the source of inflammation.
When is it ordered?
This test may be ordered when an individual is suspected of having a serious bacterial infection based on their medical history and signs and symptoms. It may be ordered, for example, when a newborn shows signs of infection or when an individual has symptoms of sepsis, such as fever, chills and rapid breathing and heart rate.
It may also be ordered on a regular basis to monitor conditions such as rheumatoid arthritis and lupus and is often repeated at intervals to determine whether treatment is effective. This is particularly useful for inflammation problems since CRP levels drop as inflammation subsides.
What does the test result mean?
The level of CRP in the blood is normally low.
A high or increasing amount of CRP in the blood suggests the presence of inflammation but will not identify its location or the condition causing it. In individuals suspected of having a serious bacterial infection, a high CRP suggests the presence of one. In people with chronic inflammatory conditions, high levels of CRP suggest a flare-up or that treatment has not been effective.
If the CRP level is initially elevated and drops, then it means that the inflammation or infection is subsiding and/or responding to treatment.
Is there anything else I should know?
CRP levels can be elevated in the later stages of pregnancy as well as with use of birth control pills or hormone replacement therapy (i.e., estrogen). Higher levels of CRP have also been observed in people who are obese.
The erythrocyte sedimentation rate (ESR) test will also be increased in the presence of inflammation; however, CRP increases sooner and then decreases more rapidly than the ESR.
Common Questions
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Article Sources
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
Sources Used in Current Review
Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. McPherson R, Pincus M, eds. Philadelphia, PA: Saunders Elsevier: 2007, Pp 224, 240.
Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry, AACC Press, Washington, DC, Pg 203.
Makover, M. (Updated 2011 February 10). C-reactive protein. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003356.htm. Accessed October 2011.
(© 1995–2011). Unit Code 9731: C-Reactive Protein (CRP), Serum. Mayo Clinic Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/9731 through http://www.mayomedicallaboratories.com. Accessed October 2011.
Rollins, G. (2009 February). The JUPITER Trial and CRP, Will the Results Change Clinical Practice? Clinical Laboratory News v 35 (2) [On-line information]. Available online at http://www.aacc.org/publications/cln/2009/February/Pages/CovStory2Feb09.aspx through http://www.aacc.org. Accessed October 2011.
Ridker, P. (2009 February). C-Reactive Protein: Eighty Years from Discovery to Emergence as a Major Risk Marker for Cardiovascular Disease. Clinical Chemistry 55:2 209–215 (2009) [On-line information]. Available online at http://www.clinchem.org/cgi/reprint/55/2/209 through http://www.clinchem.org. Accessed October 2011.
Lowry, F. (2010 March 23). CRP Test Guides Antibiotic Prescribing for Respiratory Tract Infections. From Medscape Medical News [On-line information]. Available online at http://www.medscape.com/viewarticle/719005 through http://www.medscape.com. Accessed October 2011.
Lee, C. and Hammel, J. (Updated 2011 April 15). Temporal Arteritis in Emergency Medicine. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/809492-overview through http://emedicine.medscape.com. Accessed October 2011.
Pagana, K. D. & Pagana, T. J. (© 2011). Mosby’s Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 319-321.
Sources Used in Previous Reviews
A Manual of Laboratory & Diagnostic Tests. 6th ed. Fischbach F, ed. Philadelphia: Lippincott Williams & Wilkins; 2000: 619-620.
MEDLINEplus Medical Encyclopedia. C-reactive protein. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003356.htm.
Nader Rifai, PhD. Department of Laboratory Medicine, Children's Hospital, Boston, MA.
Wu, A. (2006). Tietz Clinical Guide to Laboratory Tests, Fourth Edition. Saunders Elsevier, St. Louis, Missouri. Pp 190-193.
