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

A total LDH level may be ordered, along 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 he may order 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 ordered to monitor damage caused by muscle trauma or injury and to help identify hemolytic anemia. Hemolytic anemia is caused by the breakage of red blood cells – either because they are unusually fragile or because something is mechanically breaking them, such as an artificial heart valve.

LDH and LDH isoenzymes may still be occasionally ordered along with CK and CK-MB when a patient has symptoms of a heart attack, but this is increasingly rare. In most cases today, the doctor will order troponin levels along with the CK and CK-MB 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 a wide variety of conditions reflecting its widespread tissue distribution.

Elevated levels of LDH may be seen with:

• Cerebrovascular accident (CVA, stroke)
• Drugs: anesthetics, aspirin, narcotics, procainamides, alcohol
• Hemolytic anemias
• Pernicious anemias (megaloblastic anemais)
• Infectious mononucleosis (Mono)
• Intestinal and pulmonary infarction
• Kidney disease
• Liver disease
• Muscular dystrophy
• Pancreatitis
• Lymphoma or 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.
• Hemolysis of the blood specimen can cause falsely elevated results. This may happen if the specimen is handled roughly, stored in extreme temperatures, or if the sample was difficult to collect.
• If your platelet count is increased, serum LDH will be artificially high and not reflective of the LDH actually present.