Lactate dehydrogenase (LDH) isoenzyme test

This test measures lactate dehydrogenase (LDH) isoenzymes in a sample of your blood. It is a general test that can help determine if you have tissue damage due to illness or injury. It can also help show which organs and other tissues are likely to be damaged. But an LDH isoenzyme test alone cannot diagnose the cause of the damage.

LDH is also called lactate dehydrogenase. It's an enzyme. An enzyme is a protein that speeds up certain chemical reactions in your body. The LDH enzyme helps your cells produce energy. LDH is found in nearly every tissue in your body. The largest amounts of LDH are found in your muscles, liver, kidneys, and red blood cells.

There are five forms of the LDH enzyme that are called LDH isoenzymes. Each isoenzyme has a slightly different structure and is found in specific tissues in your body:

• LDH-1 is mostly found in your heart and red blood cells.
• LDH-2 is mostly found in your white blood cells. It's also found in your heart and red blood cells, but in smaller amounts than LDH-1.
• LDH-3 is mostly found in your lungs. Smaller amounts are found in other tissues.
• LDH-4 is mostly found in your kidneys and pancreas. If you are pregnant, it is also found in the placenta (the organ that delivers oxygen and nutrients to the baby).
• LDH-5 is mostly found in your liver and skeletal muscles (muscles that attach to your bones to help you move).

It's normal to have a small amount of LDH in your blood. But if an illness or injury damages tissue that contains LDH, the cells release LDH isoenzymes into your bloodstream and your LDH levels will rise above normal.

There are two ways to measure LDH:

• A total LDH test measures the total amount of LDH in your blood or other body fluids. It cannot tell the difference between the types of LDH isoenzymes. So, this test may show possible tissue damage, but it cannot show what tissue may be damaged.
• An LDH isoenzyme test measures the quantity of each type of isoenzyme in your blood. This information helps your health care provider determine what tissue may be damaged.

Because each LDH isoenzyme is found in more than one type of tissue, other, more specific tests are often used with or in place of an LDH isoenzyme test. These tests can more accurately identify what tissue is damaged and the condition causing the damage.

Other names: LD isoenzymes, lactate dehydrogenase isoenzyme, LDH fractionation

An LDH isoenzyme test is primarily used as a general test to check for tissue damage. It can also help determine the severity of the damage. An LDH isoenzyme test may be used to show which organs and other tissues are likely to be damaged, but other, more specific tests may be used instead.

An LDH isoenzyme test can be used with other tests to help diagnose and monitor many types of acute (sudden) and chronic (long-lasting) conditions. Conditions that can cause high LDH levels include:

• Anemia
• Kidney disease
• Liver disease including hepatitis and cirrhosis
• Pancreatitis
• A blood clot in the lung (pulmonary embolism)
• Muscular dystrophy
• A recent myocardial infarction, although troponin tests have primarily replaced LDH isoenzyme tests to diagnose heart muscle damage due to infarction

LDH isoenzyme tests can also be used to determine if treatment for many conditions is working.

The test is used to learn how serious certain types of cancer can be and whether the cancer is likely to respond to certain treatments. Regular LDH isoenzyme tests may be done to see if the cancer improves during and/or after treatment.

An LDH isoenzyme test can be used for many conditions, so it's best to ask your provider why you need this test. In general, the test is required if you:

• Do you have symptoms that suggest you have some type of tissue damage
• Have had a total LDH test that showed you have higher than normal LDH levels
• You have a condition that affects LDH levels, and your provider wants to:
  • Learn more about your condition
  • Determine if your treatment is working

You do not need special preparations for an LDH isoenzyme test.

There are very few risks in taking a blood test. You may feel a slight pain or bruise where the needle was inserted, but most symptoms go away quickly.

What your LDH isoenzyme test results mean depends on why you took the test, your symptoms, and the results of other tests you took. Ask your provider to explain what your results say about your health.

In general, a high level of one or more LDH isoenzymes It usually means that you have some type of tissue damage. The type of disease or damage depends on which LDH isoenzymes are high and how your isoenzyme levels compare to one another. For example:

• An LDH-1 that is higher than LDH-2 may be a sign of some type of anemia.
• An LDH-5 that is higher than LDH-4 may be a sign of liver damage or disease.

High levels of two or more isoenzymes may mean you have two different conditions. Or it could be a sign of cancer that has spread to different tissues.

Higher than normal levels of LDH isoenzymes don't always mean you have a medical condition that requires treatment. High levels of some LDH isoenzymes can be caused by strenuous exercise and certain medications, including aspirin. It is also possible to have high LDH isoenzymes if a lot of red blood cells exploded when your sample was taken and tested.

Lower-than-normal levels of LDH isoenzymes are not common and are not generally considered to be a health problem. Your levels of certain isoenzymes may be affected by taking large amounts of vitamin C or vitamin E. There is also a rare genetic disorder that can cause low LDH levels.

If you have questions about your results, talk to your provider.

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

1. Cleveland Clinic: Health Library: Diagnostics and Tests [Internet]. Cleveland (OH): Cleveland Clinic; c2023. LDH test; [revised April 15, 2022; cited April 7, 2023]; [approximately 12 screens]. Available at: https://my.clevelandclinic.org/health/diagnostics/22736-lactate-dehydrogenase-ldh-test
2. Farhana A, Lappin SL. Biochemistry, Lactate Dehydrogenase. [Updated May 8, 2022; cited April 7, 2023]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan. Available at: https://www.ncbi.nlm.nih.gov/books/NBK557536/
3. Hinkle J, Cheever K. Brunner & Suddarth's Handbook of Laboratory and Diagnostic Tests. 2nd ed., Kindle. Philadelphia: Wolters Kluwer Health, Lippincott Williams & Wilkins; c2014. Lactate Dehydrogenase; p. 354.
4. Lab Tests Online UK [Internet]. London (UK): The Association for Clinical Biochemistry and Laboratory Medicine; Lactate Dehydrogenase (LDH); [updated June 6, 2022; cited April 10, 2023]; [approximately 5 screens]; [approximately 5 screens]. Available at: https://labtestsonline.org.uk/tests/lactate-dehydrogenase-ldh
5. Nemours KidsHealth [Internet]. Jacksonville (FL): The Nemours Foundation; c1995-2023. Blood test: Lactate Dehydrogenase (LDH); [revised March 2023; cited April 6, 2023]; [approximately 3 screens]. Available at: https://kidshealth.org/en/parents/test-ldh.html
6. Pathology Tests Explained [Internet]. Alexandria (Australia): Australasian Association for Clinical Biochemistry and Laboratory Medicine; c2023. Lactate Dehydrogenase (LD); [Revised October 11, 2022; cited April 11, 2023]; [approximately 3 screens]. Available at: https://pathologytestsexplained.org.au/learning/test-index/ld#faq
7. Testing.com [Internet]. Seattle (WA): OneCare Media; c2023. Lactate Dehydrogenase (LDH) Test; [modified on December 1, 2022; cited on April 6, 2023]; [approximately 1 screen]. Available at: https://www.testing.com/tests/lactate-dehydrogenase-ldh/
8. UF Health: Florida Health University [Internet]. Gainesville (FL): Florida Health University; c2023. LDH isoenzyme blood test: Overview; [updated January 24, 2021; cited April 6, 2023]; [approximately 3 screens]. Available at: https://ufhealth.org/ldh-isoenzyme-blood-test
9. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2023. Health Encyclopedia: Lactate Dehydrogenase Isoenzymes; [cited April 6, 2023]; [approximately 4 screens]. Available at: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid=lactate_dehydrogenase_isoenzymes
10. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2023. Health Encyclopedia: Pulmonary Embolism; [cited April 6, 2023]; [approximately 10 screens]. Available at: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=85&contentid=p01308