Lactate is one of the substances produced by cells as the body turns food into energy (cell metabolism), with the highest level of production occurring in the muscles. Depending on pH, it is sometimes present in the form of lactic acid. However, with the neutral pH maintained by the body, most of it will be present in the blood in the form of lactate. This test measures the amount of lactate in the blood or, less commonly, in the cerebrospinal fluid (CSF).

Normally, the level of lactate in blood and CSF is low. Lactate 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 body’s cells is disrupted. Excess lactate can lead to lactic acidosis.

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 to metabolize glucose and produce ATP. This is called anaerobic energy production and the primary byproduct is lactic acid, which is processed (metabolized) by the liver.

Lactic acid can accumulate in the body and blood when it is produced faster than the liver can break it down.

Excess lactate may indicate one or a combination of the following:

• Lack of oxygen (hypoxia)
• The presence of a condition that causes increased lactate production
• The presence of a condition that causes decreased clearance of lactate from the body

When lactic acid production increases significantly, the affected person is said to have hyperlactatemia, which can then 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.