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LDH

Also known as: LD; Lactate dehydrogenase; Lactic dehydrogenase; Total LDH; LDH isoenzymes
Formal name: Lactate dehydrogenase, Total and Isoenzymes
Related tests: CK (Creatine Kinase); CK-MB; Troponin; Myoglobin

The Test Sample

What is being tested?

Lactate dehydrogenase (LDH or LD) is an enzyme that is found in almost all body tissues, but only a small amount of it is usually detectable in the blood. Contained within the tissuesÂ’ cells, LDH is released into the bloodstream when cells are damaged or destroyed. Because of this, the LDH test can be used as a general marker of injury to cells.

Elevations of LDH may be measured either as a total LDH or as LDH isoenzymes. A total LDH level is an overall measurement of 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.

Although there is some overlap, each of the five LDH isoenzymes tends to be concentrated in specific body tissues. Because of this, 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.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.