At a Glance
Why Get Tested?
To help detect hypoxia (oxygen deficiency) and other conditions that cause excess production or insufficient clearing of lactate from the blood
When to Get Tested?
The test is usually requested in emergency departments and intensive care units in patients with severe infection, sepsis, shock and other clinical situations that suggest a lack of oxygen or an acid/base imbalance. It is sometimes requested if your doctor suspects that you may have an inherited metabolic or mitochondrial disorder, or a side effect of some drugs.
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 (CSF) collected from the spine.
Test Preparation Needed?
Fasting may be required. Your doctor will let you know. You may also be told to rest prior to sample collection.
The Test Sample
What is being tested?
This test measures the amount of lactate in the blood or, more rarely, in the cerebrospinal fluid. Lactate is the ionic (electrically charged) form of lactic acid. It is produced by muscle cells, red blood cells, brain and other tissues during anaerobic energy production and is usually present in low levels in the blood. Aerobic energy production is the body’s preferred process, but it requires an adequate supply of oxygen. Aerobic energy production occurs in the mitochondria, tiny power stations inside each cell of the body that use glucose and oxygen to produce ATP (adenosine triphosphate), the body’s primary source of energy.
When cellular oxygen levels are decreased, however, and/or the mitochondria are not functioning properly, the body must turn to less efficient anaerobic energy production to metabolise glucose and produce ATP. In this process, the primary byproduct is lactic acid, which can build up faster than the liver can break it down. When lactic acid levels increase significantly in the blood, the affected person is said to have first hyperlactataemia and then lactic acidosis. The body can often compensate for the effects of hyperlactataemia, 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.
Lactic acidosis can be separated into two types: A and B.
- Type A may be due to inadequate oxygen uptake in the lungs and/or to decreased blood flow (hypoperfusion) resulting in decreased transport of oxygen to the tissues. The most common reason for this is shock from a variety of causes including trauma and blood loss, but lactic acidosis may also be due to conditions such as heart attack, congestive heart failure and pulmonary oedema (fluid in the lungs).
- Type B is caused by conditions that increase the amount of lactate/lactic acid in the blood but are not related to a decreased availability of oxygen. This includes liver and kidney disease, diabetes, leukaemia, AIDS, glycogen storage diseases (such as glucose-6-phosphatase deficiency), drugs and toxins, severe infections (both systemic sepsis and meningitis), and a variety of inherited metabolic and mitochondrial diseases (forms of muscular dystrophy that affect normal ATP production). Strenuous exercise can also result in increased blood levels of lactate.
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.
Is any test preparation needed to ensure the quality of the sample?
Your doctor will let you know if you need to fast. You may also be told not to exercise for a period of time before this test.
Ask a Laboratory Scientist
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.