Lactate Dehydrogenase (LDH) Isoenzymes Test

This test measures lactate dehydrogenase (LDH) isoenzymes in a sample of your blood. It's a general test that can help find out if you have tissue damage from disease or injury. It can also help show which organs and other tissues are likely to be damaged.

But an LDH isoenzymes test alone cannot diagnose what's causing the damage. 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. The LDH enzyme helps your cells make energy. LDH 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. There are five forms of the LDH enzyme which are called LDH isoenzymes. Each isoenzyme has a slightly different structure and is found in specific tissues in your body: LDH-1 is mainly in your heart and red blood cells.; LDH-2 is mainly in your white blood cells.

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

But if disease or injury damages tissues that contain 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 can't tell the difference between the types of LDH isoenzymes.

So, this test can show possible tissue damage, but it can't show which tissue may be damaged.; An LDH isoenzyme test measures the amount of each type of isoenzyme in your blood. This information helps your health care provider figure out which tissues 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 instead of an LDH isoenzymes test. These tests can more accurately identify which tissue is damaged and the condition causing the damage.

Why this test is done

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

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

How to prepare

You don't need any special preparations for an LDH isoenzymes test.

Sample type

Blood

Other names for this test

LD isoenzymes, lactic dehydrogenase isoenzyme, LDH fractionation