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
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:
- Shock from trauma or extreme blood loss (hypovolemia)
- Heart attack
- Congestive heart failure
- Severe lung disease or respiratory failure
- Pulmonary edema
- Severe anemia
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
- 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.
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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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