An intracellular enzyme, its main function is glycolysis, that is, to "burn" glucose with energy release.

There are 5 types of LDH found in certain organs:

• LDH-1 –  heart and red blood cells (erythrocytes)
• LDH-2 –  reticuloendothelial system (spleen, lymph nodes)
• LDH-3 – lungs
• LDH-4 –  kidney, placenta, pancreas
• LDH-5 –  liver and muscles

When above tissues are destroyed, large amount of LDH is secreted in the blood. Therefore, this test is necessary for doctors in different fields.

In case of myocardial infarction, the peak of LDH activity is observed on day 3-4, and then it remains at the same level for 10 days. If the patient has had a severe attack of angina pectoris (differs from heart attack in that there is no death of the heart muscle), then a few days after attack, the test will indicate whether the heart cells have been destructed or not.

In case of pulmonary embolism (blockage of  blood vessel with thrombus in the lungs), triad of laboratory symptoms is found: high concentration of LDH and bilirubin whereas concentration of  AST is normal. That helps to distinguish embolism from myocardial infarction.

In case of viral meningitis (inflammation of the  brain tunic), high concentration of LDH is negative - it indicates that  encephalitis develops in the patient (inflammation of the brain substance)

In case of muscle diseases, LDH indicates the cause - it increases with the death of muscle fibers and remains unchanged if the disease causes the problems in nervous system.

Severe forms of hepatitis (liver inflammation) are distinguished with high and long-term unchanging LDH concentration.

Lactate dehydrogenase helps to diagnose anemia (low hemoglobin levels in red blood cells). In case of hemolytic anemia, when red blood cells are destroyed and, as a result, hemoglobin is decreased, LDH is increased.