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Also known as: LD; Lactate dehydrogenase; Total LDH; LDH isoenzymes

At a Glance

Why Get Tested?

To help identify the cause and location of tissue damage in the body, and to monitor its progress. LDH is elevated in a wide variety of conditions reflecting its wide spread tissue distribution. Historically, has been used to help diagnose and monitor a heart attack, but troponin has replaced LDH in this role.

When to Get Tested?

Along with other tests, when your doctor suspects that you have an acute or chronic condition that is causing tissue or cellular destruction and he wants to identify and monitor the problem.

Sample Required?

A blood sample taken from a vein in your arm

Test Preparation Needed?


The Test Sample

What is being tested?

Lactate dehydrogenase (LDH, or LD) is an enzymethat is found in almost all body tissues but only a small amount of it is usually detectable in the blood. It usually stays contained within the tissues’ cells. When cells are damaged or destroyed, however, they release LDH into the bloodstream, causing blood levels to rise. For this reason, LDH is used as a general marker of injury to cells; it is not useful for determining which specific cells are damaged.

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 (slightly different molecular versions of the LDH enzyme). A total LDH level will reflect the tissue damage done 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, 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.

The Test

Common Questions

Ask a Laboratory Scientist

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.