Other names: Lactate Dehydrogenase; LDH Isoenzymes; LD; Total LDH

Lactate dehydrogenase (LDH) is an enzyme, which is found in most of the body’s cells; in a healthy individual, only very small amounts of the enzyme are detectable in the blood. LDH is released into the blood when the cells are damaged, causing levels of LDH in the blood to rise. The LDH test is a general marker for cell damage; however, the test cannot be used to determine which cells are damaged.

There are five different LDH isoenzymes; tests can measure levels of individual isoenzymes, as well as the total amount of LDH in the blood (known as the total LDH level). Different isoenzymes are usually found in different concentrations in specific tissues; this means that the test results may indicate which organs have been damaged. The five isoenzymes include LDH-1 (found mainly in the heart, kidneys and red blood cells), LDH-2 (found mainly in the heart and red blood cells), LDH-3 (found mainly in the lungs), LDH-4 (found mainly in the white blood cells, the liver and muscle cells) and Ldh-5 (found mainly in the liver and muscle cells).

When is the test used?

The test is used primarily to test for both acute and chronic tissue damage. The test may also be used to monitor conditions, which may become more advanced. The LDH isoenzyme test may also be used to help determine which organ or tissue has been damaged; however, the test is not used very often.

The test is usually ordered when a doctor suspects that a patient has sustained tissue or cellular damage.

How is the test done?

The test is done by taking a sample of blood from a vein in the arm (usually on the inside of the elbow); the blood is drawn out using a needle and syringe and the sample is collected in the syringe. The sample is then bottled, sealed, labelled and sent away to the laboratory for evaluation.

What do the test results mean?

If levels of LDH are higher than usual, this indicates some degree of tissue damage. Usually, after an injury or trauma, levels of LDH will rise after around 48 hours, reaching peak levels after 2-3 days and then start to decrease; levels usually return to normal after 10 days.

Elevated levels of LDH may be caused by several different health conditions, including:

  • Stroke
  • Some forms of anaemia (including pernicious anaemia and haemolytic anaemia)
  • Kidney disease
  • Liver disease
  • Muscular dystrophy
  • Pancreatitis
  • Glandular fever
  • Certain forms of cancer
  • Certain types of drug (including aspirin and anaesthetics)

Normal and low levels of LDH are usually not a cause for concern.

Levels of LDH may increase after strenuous physical exercise.

Specific Blood Tests

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