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Enzymes Movie

This blood test measures the blood levels of the fractions (or isoenzymes) of the enzyme lactic dehydrogenase, also called LDH.

LDH is found in many body tissues and organs. Tissue or organ injury can release LDH into the bloodstream, thereby raising the level. The test is usually done to see if tissue or organ damage has occurred.

In the past, LDH isoenzymes were most commonly used to evaluate patients for heart attacks. However, the troponin test has been the test of choice and is much more specific.

Who is a candidate for the test?

A doctor may order this test if he or she suspects tissue damage in the body.

How is the test performed?

In order to measure the amounts of LDH isoenzymes in the blood, a blood sample is taken from a vein on the forearm or hand. First, the skin over the vein is cleaned with an antiseptic. Next, a rubber tube is tied around the upper arm to enlarge the veins in the lower arm. A fine needle is gently inserted into a vein, and the tourniquet is removed. Blood flows from the vein through the needle and is collected in a syringe or vial to be tested in the lab. After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.

What is involved in preparation for the test?

No preparation is normally required for this test.

What do the test results mean?

• heart attack, or heart muscle damage from a blockage in a heart artery
• hemolytic anemia, a condition in which red blood cells are destroyed
• infectious mononucleosis, an infection caused by a virus called the Epstein-Barr virus
• intestinal damage
• liver disease, such as cirrhosis
• low blood pressure
• lung damage
• muscle injury
• new abnormal tissue formation
• pancreatitis, or inflammation of the pancreas
• stroke, or damage to the brain caused by a lack of oxygen