Definition This test measures the levels of the different forms of the enzyme called lactic dehydrogenase, or LDH, in the blood. These different forms are called isoenzymes.
LDH isoenzymes are in many body tissues and organs. Tissue or organ injury can release LDH isoenzymes into the bloodstream, thereby raising their levels. The test is usually done to see if tissue or organ damage has occurred.
Who is a candidate for the test? A doctor may order this test if he or she suspects a heart attack or other 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 strong rubber tube is wrapped 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 analysed in the laboratory. After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.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? Normal levels of LDH isoenzymes are:
total LDH: 115-225 IU/L (international units per litre)
LDH-1: 17-27% of the total amount
LDH-2: 27-37% of the total amount
LDH-3: 18-25% of the total amount
LDH-4: 8-15% of the total amount
LDH-5: 5-15% of the total amount
Abnormally high levels of LDH isoenzymes may indicate:
heart attack, or heart muscle damage from a blockage in a heart artery
haemolytic anaemia, a condition in which red blood cells are destroyed
stroke, or damage to the brain caused by a lack of oxygen
LDH-1 levels that are higher than LDH-2 often indicate that a heart attack has recently occurred.
There are now more specific blood tests to indicate a recent heart attack, such as Troponin levels.
Author: David T. Moran, MD Reviewer: eknowhow Medical Review Panel Editor: Dr John Hearne Last Updated: 6/06/2005 Contributors Potential conflict of interest information for reviewers available on request
