Blood lactic acid concentration may be measured to detect and monitor impaired circulation and tissue oxygenation in critically ill patients, such as patients experiencing septic shock. When cells do not receive enough oxygen because they are not receiving enough blood, they release excess lactic acid into the bloodstream. Organ failure as a result of septic shock may be indicated by unexplained metabolic acidosis (low blood pH and low bicarbonate level) and extremely elevated lactic acid, where blood pH is <7.30 and plasma lactic acid is >1.5 times the upper limit of the laboratory’s established reference values.
Lactic acid can be produced in all tissues, especially skeletal muscle, brain, erythrocytes, and kidneys. In homeostasis, lactic acid clears very quickly through liver metabolism and reconversion of lactate back to pyruvate. This process results in minimal lactic acid levels in normal arterial and venous blood samples.