Lactate Dehydrogenase (LDH)

LDH is also called lactic acid dehydrogenase. It is an enzyme. An enzyme is a protein that speeds up certain chemical reactions in your body. LDH helps your cells make energy. It is found in almost all the tissues in your body. The largest amounts of LDH are found in your muscles, liver, kidneys, and red blood cells.

If disease or injury damages tissues that have LDH, their cells release the enzyme into your bloodstream or other body fluids. It's normal to have some LDH in your blood and body fluids. But if your LDH levels are high, it may be a sign of certain diseases or injuries.

Because LDH is found in so many tissues throughout your body, the test on its own can't show what is damaging your tissues or where the damage is located. So, an LDH test is usually done with other types of tests that can help pinpoint the problem. In some cases, isoenzyme analysis can be used to narrow down which tissue is the source of an elevation.

LDH testing is used for many reasons. The meaning of your LDH test results depends on the reason you had the test, your symptoms, and the results of other tests you've had. So, ask your provider to explain what your results say about your health.

In general, LDH levels that are higher than normal usually mean you have some type of tissue damage. The damage is usually from disease, infection, or injury. Specific causes can include heart attack, liver disease, certain anemias (such as megaloblastic anemia), blood clots in the lungs, some cancers, and muscular dystrophy. Your provider may order more tests to diagnose your condition.

But a higher than normal LDH level doesn't always mean you have a medical condition that needs treatment. High levels can be caused by intense exercise and certain medicines, including aspirin. It's also possible to have a high LDH level if many red blood cells broke open when your sample was collected and tested.

Lower than normal LDH levels aren't common and usually aren't considered to be a health problem. Taking large doses of vitamin C (ascorbic acid) supplements before a blood draw can interfere with the lab test and make your LDH result look lower than it really is — this is a testing issue, not a true drop in LDH. Low LDH levels may also be caused by a rare genetic disorder called lactate dehydrogenase deficiency.