What is a lactate dehydrogenase (LDH) test?

A lactate dehydrogenase (LDH) test usually measures the level of lactate dehydrogenase (LDH) in a sample of your blood. In certain cases, LDH levels are measured in samples of other body fluids. This includes testing fluid from the spine (cerebrospinal fluid), the belly (peritoneal fluid), and the chest (pleural fluid).

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.

An LDH test alone 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 diagnose the problem.

Other names: LD test, lactic dehydrogenase, lactic acid dehydrogenase

What is it used for?

LDH is mainly used to check for tissue damage. Many types of acute (sudden) and chronic (long-lasting) conditions can damage tissues and cause high LDH levels. So LDH testing may be used in many different situations from bone and muscle injuries to monitoring treatment for cancer. For example, an LDH test may be used to:

• Help diagnose and/or monitor diseases that affect the:
  • Blood, including anemia
  • Liver
  • Lungs
  • Kidneys
  • Heart, including heart attack
  • Pancreas
  • Brain and spinal cord, such as encephalitis and bacterial meningitis
• Help monitor conditions that may get worse over time, such as muscular dystrophy and HIV
• Help diagnose certain severe infections
• Find out how serious certain types of cancer may be, including multiple myeloma, lymphoma, leukemia, testicular cancer, and melanoma.
• Check whether treatment for certain types of cancer is working

Why do I need an LDH test?

Because LDH testing is used for so many conditions, it's best to ask your health care provider why you need an LDH test. In general, the test is ordered if other tests and/or your symptoms suggest you have tissue damage or disease.

If you have a disease that affects LDH levels, you may need an LDH test to learn more about your condition and to find out if your treatment is helping.

What happens during an LDH test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

If your provider thinks you have a condition that may affect LDH levels in other body fluids, you may have a procedure to get a fluid sample. These procedures may include:

• A lumbar puncture or "spinal tap" to collect cerebrospinal fluid that flows around your brain and spinal cord
• A thoracentesis to remove fluid in the chest
• A paracentesis or "abdominal tap" to remove fluid from the abdomen

If you are having one of these tests, your provider will explain the procedure.

Will I need to do anything to prepare for the test?

You don't need any special preparations for an LDH blood test. If your test uses other fluid samples, your provider will tell you how to prepare.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly. If you are having another type of test, your provider will explain the risks.

What do the results mean?

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. Your provider may order more tests to diagnose your condition.

But higher a 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 amounts of vitamin C or vitamin E may cause low levels. Low LDH levels may also be caused by a rare genetic disorder called lactate dehydrogenase deficiency.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about an LDH test?

If your results showed higher than normal LDH levels, your provider may order a more specific type of LDH test that can help find out where the LDH is coming from. This more specific test is called an LDH isoenzyme test.

An LDH isoenzyme test measures the levels of five different forms of LDH. This information helps your provider find out about the type of tissue that's damaged, where in the body it may be, and how serious the damage may be.