Lactate dehydrogenase (LDH)

Currently, the main use for LDH is as a general indicator of the existence and severity of acute or chronic tissue damage and, sometimes used to monitor progressive conditions. LDH isoenzymes may also be used to help determine which organs are likely to be involved but this test is rarely available.

The overall use of LDH and LDH isoenzymes has decreased. Traditionally, they were most frequently used, with other tests such as CK and CK-MB, to help diagnose and monitor myocardial infarctions (heart attacks). This use of LDH, however, has been almost entirely replaced by troponin measurements in recent years because troponin is better and more specific and sensitive to heart tissue injury than LDH.

A total LDH level may be used with other tests, as a screening test when your doctor suspects some kind of cellular or tissue damage. If the total LDH is elevated, then the doctor may request LDH isoenzymes, or more commonly other tests such as ALT, AST or ALP to help diagnose the condition and to help determine which organs are involved. Once the acute or chronic problem is diagnosed, total LDH levels may be used at regular intervals to monitor its progress and/​or resolution.

LDH levels may also occasionally be used to monitor damage caused by muscle trauma or injury and to help identify haemolytic anaemia (anaemia caused by the breakdown of red blood cells – either because the cells are unusually fragile or because something is mechanically damaging them, such as an artificial heart valve).

When a patient has symptoms of a heart attack, troponin levels are used instead of LDH.

Elevated levels of LDH and changes in the ratio of the LDH isoenzymes usually indicate some type of tissue damage. Usually LDH levels will rise as the cellular destruction begins, peak after some time period, and then begin to fall. For instance, when someone has a heart attack, blood levels of total LDH will rise within 24 to 48 hours, peak in 2 to 3 days, and return to normal in 10 to 14 days. LDH levels are elevated in many other conditions reflecting its widespread tissue distribution.

Elevated levels of LDH may be seen with:

• Cerebrovascular accident (CVA, stroke)
• Drugs: anaesthetics, aspirin, narcotics, procainamides, alcohol
• Haemolytic anaemia
• Pernicious anaemias (megaloblastic anaemais)
• Infectious mononucleosis (glandular fever)
• Intestinal and pulmonary infarction (tissue death)
• Kidney disease
• Liver disease
• Muscular dystrophy
• Pancreatitis
• Some cancers
• Lymphoma and other cancers

With some chronic and progressive conditions, and some drugs, moderately elevated LDH levels may persist.

Low and normal levels of LDH do not usually indicate a problem. Low levels are sometimes seen when a patient ingests large amounts of ascorbic acid (vitamin C).

Many things can affect LDH results that are not necessarily a cause for concern. For example:

• Strenuous exercise can cause temporary elevations in LDH.
• Haemolysis of the blood specimen can cause false positives (“haemolysis of blood” refers to breakage of red blood cells in the blood sample which may happen if the specimen is handled roughly, stored in extreme temperatures or if the specimen was difficult to collect).
• If your platelet count is increased, serum LDH will be artificially high and not reflective of the LDH actually present.

Several of the LDH isoenzymes may rise at the same time if more than one organ is involved as, for example, in the case of a patient who has pneumonia, and then suddenly has a heart attack. In another example, more than one LDH isoenzyme might rise if a patient has a progressive disease such as metastatic cancer that is affecting multiple organs. Although the different LDH isoenzymes are concentrated in specific tissues, there is some overlap in where they are found. A single cause may elevate several of them to some degree. For instance, vigorous exercise may temporarily elevate LDH‑1, LDH‑2, and LDH‑5.