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 metabolize 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 hyperlactatemia and then lactic acidosis (LA). The body can often compensate for the effects of hyperlactatemia, but LA 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 is 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 LA may also be due to conditions such as heart attack, congestive heart failure, and pulmonary edema (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, leukemia, 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.
