Lactate dehydrogenase (LDH) | Pathology Tests Explained

What is being tested?

Lactate dehydrogenase (LD) is an enzyme that is found in cells throughout the body.

Only a small amount of LD is usually detectable in the blood. However, when cells are damaged or destroyed, they release LD into the bloodstream, causing blood levels to rise. For this reason, LD is used as a general marker of injury to cells. This also happens when blood cells are destroyed in the bloodstream, such as in a form of anaemia known as haemolytic anaemia.

In the past, special tests were performed to work out which type of tissue the LD was released from. These tests, known as `LD isoenzymes’ are not performed routinely anymore because there are more specific tests available.

How is it used?

The main use for LD is as a general indication of cell damage, including muscle damage, liver damage, blood cell damage and cancers. In the past, LD was used to help diagnose and monitor myocardial infarctions (heart attacks) but it has been replaced by a better test, troponin (more specific and sensitive to heart tissue injury than LD).

In people with progressive conditions, including melanoma, LD can be tested at regular intervals to monitor the progress of the condition.

When is it requested?

LD may be used as a screening test when some kind of cellular or tissue damage is suspected. If the LD is high other, more specific tests such as CK, ALT and AST can be used to help pinpoint the organs involved. Once the problem is diagnosed, LD levels may be tested at regular intervals to monitor its progress.

LD levels can also occasionally be ordered when someone has experienced muscle trauma or injury. They can also be ordered when someone has signs and symptoms of haemolytic anaemia.

LD testing may be ordered on a regular basis when someone has been diagnosed with cancer.

What does the result mean?

High levels of LD usually indicate some type of tissue damage. Usually LD levels rise as the cell destruction begins, peak after some time and then begin to fall. As an example, when someone has a heart attack, blood levels of total LD rise within 24 to 48 hours, peak in two to three days and return to normal in 10 to 14 days.

Elevated levels of LD may be seen with:

Anaemias including haemolytic anaemia
Pernicious anaemias (megaloblastic anaemia)
Infections including infectious mononucleosis (glandular fever), tuberculosis and serious fungal infections
Intestinal and lung infarction (tissue death)
Liver disease including hepatitis
Muscle damage
Pancreatitis
Some cancers including melanoma
Cerebrovascular accident (CVA, stroke)
Drugs including anaesthetics, narcotics, methotrexate

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

Low levels of LD do not usually indicate a problem.

Reference intervals

Adult
120 -250 U/L

The reference intervals shown above are known as a harmonised reference interval. This means that eventually all laboratories in Australia will eventually use this same interval so wherever your sample is tested, the reference interval should be the one shown above. Laboratories are in the process of adopting these harmonised intervals so it is possible that the intervals shown on the report of your results for this test may be slightly different until this change is fully adopted.

Is there anything else I should know?

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

Strenuous exercise can cause temporary elevations in LD
Damage to the sample during and after collection can cause falsely elevated results by causing breakage of red blood cells in the sample (haemolysis)
If the platelet count is increased, serum LD will be artificially high and not reflective of the LD actually present.

Common questions