Lactate

A metabolic product of glycolysis that is formed in greater amounts when pyruvate is not used quickly enough in the mitochondria. The lactate/pyruvate ratio is looked at with questions about energy metabolism. Raised with intense exercise, hypoxia or mitochondrial pathology.

What lactate does in the body

Lactate is formed in the cytoplasm when lactate dehydrogenase converts pyruvate with the help of NADH; this regenerates NAD⁺, which glycolysis needs in order to continue. This does not only happen when oxygen is lacking: red blood cells have no mitochondria and obtain their energy exclusively by this route, and muscles working rapidly also produce more lactate than they can use immediately. Lactate is not waste but a fuel that travels between the organs: the heart, resting muscles, kidneys and brain convert it back into pyruvate and burn it in their mitochondria, and the liver rebuilds it into glucose in the Cori cycle.

Low lactate – what does it mean?

Low values are the normal case at rest: lactate is used roughly as fast as it is formed, because enough oxygen is available and the mitochondria take up pyruvate promptly. On a low-carbohydrate diet, during fasting or after long endurance exercise with depleted glycogen stores, less lactate is also formed, because glycolysis then processes less glucose. Low values usually have no pathological significance of their own.

High lactate – what happens in the body?

When lactate rises, it is being formed faster than the liver, heart and muscles can break it down. During intense exertion, the oxygen in the working muscles is no longer sufficient, and glycolysis supplies ATP by the fast route via lactate. At rest, a raised value shows that pyruvate is entering the mitochondria or being used there less well – for example with a lack of oxygen in the tissues due to circulatory or lung disease or severe anaemia, with vitamin B1 deficiency, with disorders of the respiratory chain or with medications such as metformin; reduced liver function also slows breakdown. Hydrogen ions accumulate together with the increased lactate production. Very high amounts acidify the blood (lactic acidosis), which shows as rapid breathing, nausea and weakness – that is an emergency.

The interpretation is given in your report.