Also Known As
Lactate dehydrogenase
Total LDH
LDH isoenzymes
Formal Name
This article was last reviewed on
This article waslast modified on 13 June 2022.
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 wants to identify and monitor the problem.

Sample Required?

A blood sample taken from a vein in your arm

Test Preparation Needed?


What is being tested?

Lactate dehydrogenase (LDH, or LD) is an enzyme found in almost all body tissues. Usually the concentration of LDH in the blood is low, because  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. Isoenzymes are slightly different molecular versions of the same enzyme. A total LDH level is an overall measurement of five different LDH isoenzymes. A high total LDH level reflects tissue damage but it is not specific to any one type of tissue, and so, 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 (smaller 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.

Accordion Title
Common Questions
  • How is it used?

    Currently, the main use for LDH is as a general indicator of the existence and severity of acute or chronic tissue damage and, sometimes used to monitor progressive conditions. LDH isoenzymes may also be used to help determine which organs are likely to be involved but this test is rarely available.

    The overall use of LDH and LDH isoenzymes has decreased. Traditionally, they were most frequently used, with other tests such as CK and CK-MB, to help diagnose and monitor myocardial infarctions (heart attacks). This use of LDH, however, has been almost entirely replaced by troponin measurements in recent years because troponin is better and more specific and sensitive to heart tissue injury than LDH.

  • When is it requested?

    A total LDH level may be used with other tests, as a screening test when your doctor suspects some kind of cellular or tissue damage. If the total LDH is elevated, then the doctor may request LDH isoenzymes, or more commonly other tests such as ALT, AST or ALP to help diagnose the condition and to help determine which organs are involved. Once the acute or chronic problem is diagnosed, total LDH levels may be used at regular intervals to monitor its progress and/or resolution.

    LDH levels may also occasionally be used to monitor damage caused by muscle trauma or injury and to help identify haemolytic anaemia (anaemia caused by the breakdown of red blood cells – either because the cells are unusually fragile or because something is mechanically damaging them, such as an artificial heart valve).

    When a patient has symptoms of a heart attack, troponin levels are used instead of LDH.

  • What does the test result mean?

    Elevated levels of LDH and changes in the ratio of the LDH isoenzymes usually indicate some type of tissue damage. Usually LDH levels will rise as the cellular destruction begins, peak after some time period, and then begin to fall. For instance, when someone has a heart attack, blood levels of total LDH will rise within 24 to 48 hours, peak in 2 to 3 days, and return to normal in 10 to 14 days. LDH levels are elevated in many other conditions reflecting its widespread tissue distribution.

    Elevated levels of LDH may be seen with:

    With some chronic and progressive conditions, and some drugs, moderately elevated LDH levels may persist.

    Low and normal levels of LDH do not usually indicate a problem. Low levels are sometimes seen when a patient ingests large amounts of ascorbic acid (vitamin C).

  • Is there anything else I should know?

    Many things can affect LDH results that are not necessarily a cause for concern. For example:

    • Strenuous exercise can cause temporary elevations in LDH.
    • Haemolysis of the blood specimen can cause false positives (“haemolysis of blood” refers to breakage of red blood cells in the blood sample which may happen if the specimen is handled roughly, stored in extreme temperatures or if the specimen was difficult to collect).
    • If your platelet count is increased, serum LDH will be artificially high and not reflective of the LDH actually present.
  • Why would more than one LDH isoenzyme be elevated?

    Several of the LDH isoenzymes may rise at the same time if more than one organ is involved as, for example, in the case of a patient who has pneumonia, and then suddenly has a heart attack. In another example, more than one LDH isoenzyme might rise if a patient has a progressive disease such as metastatic cancer that is affecting multiple organs. Although the different LDH isoenzymes are concentrated in specific tissues, there is some overlap in where they are found. A single cause may elevate several of them to some degree. For instance, vigorous exercise may temporarily elevate LDH-1, LDH-2, and LDH-5.