Lactate

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Also known as: Lactic Acid; L-Lactate
Formal name: Lactate
Related tests: Blood Gases, Pyruvate, CSF Analysis, CMP, BMP, Electrolytes

At a Glance

Why Get Tested?

To detect high levels of lactate in the blood, which may be an indication of lack of oxygen (hypoxia) or the presence of other conditions that cause excess production or insufficient clearing of lactate from the blood; this test is not meant to be used for screening for health status.

When to Get Tested?

When someone has symptoms such as rapid breathing, nausea, and sweating that suggest a lack of oxygen or an acid/base imbalance; when a person presents with what a doctor suspects is sepsis, shock, heart attack, severe congestive heart failure, renal failure, or uncontrolled diabetes; when a doctor suspects that someone has an inherited metabolic or mitochondrial disorder

Sample Required?

A blood sample drawn from a vein in your arm; sometimes a blood sample collected from an artery and, rarely, a sample of cerebrospinal fluid collected from the spine

Test Preparation Needed?

You may be told to rest prior to sample collection. Rarely, fasting may be required.

The Test Sample

What is being tested?

This test measures the amount of lactate in the blood or, more rarely, in the cerebrospinal fluid (CSF). Lactate is a product of cell metabolism. Depending on pH, it is sometimes present in the form of lactic acid. However, with the neutral pH of the body, most of it will be present in the form of lactate.

Normally, the level of lactate in blood and CSF is low. It is produced in excess by muscle cells, red blood cells, brain, and other tissues when there is insufficient oxygen at the cellular level or when the primary way of producing energy in the cells is disrupted.

The principal means of producing energy within cells occurs in the mitochondria, tiny power stations inside most cells of the body. The mitochondria use glucose and oxygen to produce ATP (adenosine triphosphate), the body's primary source of energy. This is called aerobic energy production.

Whenever cellular oxygen levels decrease and/or the mitochondria are not functioning properly, the body must turn to less efficient energy production (anaerobic energy production) to metabolize glucose and produce ATP. The primary byproduct of this anaerobic process is lactic acid. Lactic acid can accumulate when it is produced faster than the liver can break it down.

When lactic acid levels increase significantly in the blood, the affected person is said to have hyperlactatemia, which can progress to lactic acidosis as more lactic acid accumulates. The body can often compensate for the effects of hyperlactatemia, but lactic acidosis can be severe enough to disrupt a person's acid/base (pH) balance and cause symptoms such as muscular weakness, rapid breathing, nausea, vomiting, sweating, and even coma.

There are a number of conditions that can cause high levels of lactate. They are separated into two groups according to the mechanism by which they cause lactic acidosis.

Type A lactic acidosis, the most common type, may be due to conditions that cause inadequate oxygen uptake in the lungs and/or to reduced blood flow resulting in decreased transport of oxygen to the tissues (decreased tissue perfusion). Examples of type A conditions include:

Type B lactic acidosis is not related to delivery of oxygen but reflects excess demand for oxygen or metabolic problems. Examples of type B causes include:

  • Liver disease
  • Kidney disease
  • Uncontrolled diabetes
  • Leukemia
  • AIDS
  • Glycogen storage diseases (such as glucose-6-phosphatase deficiency)
  • Drugs and toxins such as salicylates, cyanide, methanol and metformin
  • A variety of inherited metabolic and mitochondrial diseases that are forms of muscular dystrophy and affect normal ATP production
  • Strenuous exercise, as with marathon runners

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm. Sometimes, an arterial sample is collected by inserting a needle into an artery. Occasionally, a sample of cerebrospinal fluid is collected from the spinal column during a procedure called a spinal tap.

Blood lactate levels will usually be drawn either without the use of a tourniquet or with a tourniquet that is not released during the blood draw. Tourniquet use and release and clenching of the fist can increase lactate levels in the blood sample.

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?

In general, no test preparation is needed. In some cases, the doctor may request that you rest prior to the collection. Rarely, fasting is requested.

The Test

How is it used?

The lactate test is primarily ordered to help determine if someone has lactic acidosis, a high level of lactate in the blood. Lactate is a product of cell metabolism. Depending on pH, it is sometimes present in the form of lactic acid. However, with the neutral pH of the body, most of it will be present in the form of lactate.

Lactic acidosis is most commonly caused by an inadequate amount of oxygen in cells and tissues (hypoxia). If someone has a condition that may lead to a decreased amount of oxygen delivered to cells and tissues, such as shock or congestive heart failure, this test can be used to help detect and evaluate the severity of hypoxia and lactic acidosis. It may be ordered along with blood gases to evaluate a person's acid/base balance and oxygenation.

As lactic acidosis may also be caused by conditions unrelated to oxygen levels, this test may be used to evaluate someone who has a disease that can lead to increased lactate levels and who has signs and symptoms of acidosis. It may be ordered along with groups of tests, such as the Comprehensive Metabolic Panel, Basic Metabolic Panel, or Complete Blood Count, to determine if the underlying condition, such as liver or kidney disease, is causing lactic acidosis.

In particular, this test may be used as part of an initial evaluation of someone who is suspected of having sepsis. Typically, if their lactate level is above normal limits, treatment will be initiated without delay. If a person with sepsis can be diagnosed and treated promptly, their chances of recovery are significantly improved.

In a person being treated for an acute condition, such as sepsis, shock or heart attack, or a chronic condition, such as severe congestive heart failure, lactate levels may be ordered at intervals to help monitor hypoxia and response to treatment.

A cerebrospinal fluid (CSF) lactate test may be ordered, along with a blood lactate test, to help distinguish between viral and bacterial meningitis.

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When is it ordered?

A lactate test may be ordered when someone has symptoms of inadequate oxygen (hypoxia) such as:

  • Shortness of breath
  • Rapid breathing
  • Paleness
  • Sweating
  • Nausea
  • Muscle weakness
  • Abdominal pain
  • Coma

The test may be ordered when a person presents with what the doctor suspects is sepsis, shock, heart attack, severe congestive heart failure, renal failure, or uncontrolled diabetes. The lactate test will be initially ordered with other tests to help evaluate a person's condition and then, if significantly elevated, at intervals to monitor the condition.

CSF and blood lactate levels may be ordered when a person has symptoms of meningitis, such as severe headaches, fever, delirium, and loss of consciousness.

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What does the test result mean?

Looking for reference ranges?

A high lactate level means that the disease or condition a person has is causing lactate to accumulate. In general, the greater the increase in lactate, the greater the severity of the condition. When associated with hypoxia, an increase in lactate can indicate that organs are not functioning properly (organ dysfunction).

However, the presence of excess lactate is not diagnostic – it does not pinpoint the cause of the increase – but it does help the doctor to confirm or rule out possible reasons for the symptoms a person is experiencing. A doctor must consider a person's medical history, physical examination, and results of other diagnostic tests to pinpoint the cause and to diagnose the underlying condition or disease.

In a person who has or is suspected of having a condition that may lead to a lack of oxygen, a high lactate level may indicate some degree of hypoxia and/or organ dysfunction. Some of these conditions include:

A high lactate (lactic acidosis) may be a complication resulting from one of the following diseases or conditions:

  • Liver disease
  • Kidney disease
  • Uncontrolled diabetes
  • Leukemia
  • AIDS
  • Glycogen storage diseases (such as glucose-6-phosphatase deficiency)
  • Drugs and toxins such as salicylates, cyanide, methanol and metformin
  • A variety of rare inherited metabolic and mitochondrial diseases that are forms of muscular dystrophy and affect normal ATP production
  • Strenuous exercise, as with marathon runners

When a patient is being treated for lactic acidosis or hypoxia, decreasing concentrations of lactate over time reflect a response to treatment.

When someone has signs and symptoms of meningitis, significantly increased cerebrospinal fluid lactate levels suggest bacterial meningitis while normal or slightly elevated levels are more likely to be due to viral meningitis.

The lactate test measures the level of lactate in the blood at a given point in time. A normal level indicates that a person does not have lactic acidosis, that there is sufficient oxygen at the cellular level and/or their symptoms are not caused by lactic acidosis.

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Is there anything else I should know?

Increased lactate levels may be seen with thiamine (vitamin B1) deficiency.

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Common Questions

1.  Is there anything I can do to decrease my lactate levels?

Generally, no. However, if your elevated lactate levels are due to an underlying condition that can be addressed, such as uncontrolled diabetes or a substance that can be avoided, such as ethanol, then you may be able to lower them. If you have been diagnosed with a condition, such as a metabolic disorder, following your prescribed treatment regimen should control your lactate levels. If the increase is due to a temporary condition, such as shock or infection, then they will usually return to normal after the condition has been resolved.

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2.  Why would my doctor choose to measure arterial lactate rather than venous lactate?

Lactate measurements from arterial blood are thought to be more accurate and, because a tourniquet is not used, they are not generally affected by the collection process. Your doctor may order an arterial lactate for these reasons or because arterial blood gases are also being collected and the same sample can be used. When other arterial blood tests are not being ordered, the doctor may order a venous lactate because it gives him an adequate evaluation of your lactate concentrations and because the collection process is not as uncomfortable.

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3.  Are there other ways to measure lactate?

Yes. Lactate may be measured using a small hand-held device much like a glucose meter at the point of care (POC, at a patient's bedside) instead of in a laboratory. This type of monitoring is useful, for example, in emergency departments and intensive care units where rapid results are vital to the care of critically ill people. However, since the methods of measurement are different, the results from lactate POC tests may not be comparable with those from tests performed in a laboratory. 

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4.  What is the lactate/pyruvate ratio and how is it used?

A lactate/pyruvate ratio is a calculated result that may be used to differentiate between causes of lactic acidosis.

Pyruvate is a substance used by cells in addition to lactate in the production of energy. The mitochondria within cells metabolize glucose in a series of steps to produce ATP, the body's energy source. One of the steps involves pyruvate and the following step requires oxygen. When the oxygen level is low, pyruvate accumulates, which in turn is converted to lactate, resulting in an accumulation of lactate and lactic acidosis. The alternative cause is when there is impaired mitochondrial function and the pathway is interrupted, resulting in increased pyruvate and hence more lactate. The lactate/pyruvate ratio will be high in these cases. 

However, there are certain congenital disorders (inborn errors of metabolism) in which pyruvate is not converted to lactate. One example is pyruvate dehydrogenase deficiency. In these cases, pyruvate will accumulate, the blood level will be high, and the lactate to pyruvate ratio will be low. 

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Article Sources

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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.

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