Lactate dehydrogenase (LDH)
Why this test?
- For the diagnosis of acute or chronic tissue damage during a comprehensive examination of the patient. For differential diagnosis of diseases with sharp chest pain (myocardial infarction, angina pectoris, pulmonary infarction).
- To detect diseases accompanied by hemolysis of erythrocytes.
- For the purpose of monitoring the course of oncological diseases during therapy.
- For the study of pathologies of the liver and kidneys.
- For diagnosis of muscle tissue lesions.
In what cases is it prescribed?
- In case of suspicion of acute or chronic tissue and cell damage in the body.
- During a comprehensive preventive examination of the patient.
- When monitoring the course of some chronic diseases (muscular dystrophy, hemolytic anemia, liver and kidney diseases), oncological pathology.
Lactate dehydrogenase (LDH) is a zinc-containing intracellular enzyme that catalyzes the oxidation of lactic acid to pyruvate and is found in almost all body cells. LDH is most active in skeletal muscle, heart muscle, kidney, liver and erythrocytes.
There are five different forms (isoenzymes) of LDH, which differ in molecular structure and location in the body. Which of the five forms prevails depends on the main method of glucose oxidation - aerobic (to CO2 and H2O) or anaerobic (to lactic acid). Such a difference is due to the different degree of affinity of this or that isoenzyme and pyruvic acid. For myocardium and brain tissue, the main one is LDH-1, for erythrocytes, platelets, kidney tissue - LDH-1 and LDH-2. LDH-3 predominates in the lungs, spleen, thyroid and pancreas, adrenal glands, and lymphocytes. LDH-4 is found in all tissues with LDH-3, as well as in granulocytes, placenta and male germ cells, which also contain LDH-5. Isoenzyme activity in skeletal muscles (in descending order): LDH-5, LDH-4, LDH-3. LDH-5 isoenzyme is most characteristic for the liver, LDH-4 is less active.
Normally, all fractions of the enzyme are determined with low activity in the total indicator - total LDH. Their activity in the blood is distributed as follows: LDH-2; LDH-1; LDH-3; LDH-4; LDH-5. In diseases accompanied by tissue damage and cell destruction, the activity of LDH in the blood increases. In this regard, it is an important marker of tissue destruction.
Despite the fact that an increase in enzyme activity does not indicate any specific disease, its determination in combination with other laboratory tests helps in the diagnosis of lung infarction, muscular dystrophy and hemolytic anemia. Increased activity of LDH can be detected in newborns, pregnant women and after intense physical exertion.
Previously, joint tests for LDH, aspartate aminotransferase and creatine kinase were widely used in the diagnosis of myocardial infarction. Now, for this purpose, the level of troponin is determined as a more specific marker of damage to the heart muscle.
But the study of LDH activity remains an auxiliary analysis in the differential diagnosis of chest pain syndrome. In patients with angina pectoris, the activity of the enzyme does not change, but with a myocardial infarction, it begins to increase after 8-10 hours with a maximum in the first 24-48 hours after a heart attack and returns to normal after 10-12 days. An increase in LDH with normal AST activity 1-2 days after chest pain indicates a lung infarction.
In the differential diagnosis of myopathies, this analysis helps clarify the pathophysiological mechanisms of the disease. For example, when muscle function is impaired due to neurogenic diseases, LDH does not increase, but when muscles are damaged due to endocrine and metabolic pathologies, LDH activity increases. The activity of LDH in the blood can increase as a result of many malignant neoplasms, with effective treatment it decreases, which is sometimes used for dynamic monitoring of cancer patients.