Also known as: Lactic Acid Dehydrogenase Isoenzymes, LD Isoenzymes, LDH Isoenzymes.

Lactate dehydrogenase (LDH or LD) is an enzyme that is found in almost all body tissues with only a small amount of LD that can usually detectable in the blood. LDH is released into the bloodstream when cells are damaged and/or destroyed. This test can be used as a general marker of injury to cells.

Elevations are measured either as a total LDH or as LDH isoenzymes. A total LDH level measures five different LDH isoenzymes. Isoenzymes are slightly different molecular versions of the LDH enzyme. A total LDH level will reflect the presence of tissue damage, but it is not specific. By itself, it cannot be used to identify the underlying cause or its location. Measurements of the individual LDH isoenzyme levels can be used, along with other tests, to help determine the disease or condition causing cellular damage and to help identify the organs and tissues involved. In general, the isoenzyme locations tend to be LDH-1, heart, red cells, kidney, germ cells, LDH-2, heart, red blood cells, kidney (lesser amounts than LDH-1),LDH-3, lungs and other tissues, LDH-4, white blood cells, lymph nodes; muscle, liver (lesser amounts than LDH-5) , LDH-5, liver, skeletal muscle. While all of the isoenzymes are represented in the total LDH, LDH-2 usually makes up the greatest percentage.