Severe oxygen deprivation of tissues results in a switch from aerobic to anaerobic metabolism. Because lactate is the main product of anaerobic metabolism, it accumulates when there is oxygen deprivation.

Hypoxia seen in shock, congestive heart failure (or any other condition that would cause problems in oxygen being picked up by or transported in the blood), hepatic (liver) dysfunction, ischemia (not enough oxygenated blood getting to a certain area), and pulmonary (lung) insufficiency are all associated with increased serum lactate.