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Lactate Dehydrogenase (LDH) Isoenzymes Test
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Lab Tests

Lactate Dehydrogenase (LDH) Isoenzymes Test

The LDH isoenzymes test identifies which specific tissues or organs in your body may be damaged by measuring the five different forms of the LDH enzyme.

Overview

Lactate dehydrogenase (LDH) is an enzyme found in almost all body tissues that helps cells produce energy. When tissues are damaged by disease or injury, they release LDH into the bloodstream. There are five forms of this enzyme, known as isoenzymes, which are concentrated in specific areas:

  • LDH-1: Heart and red blood cells.
  • LDH-2: White blood cells, heart, and red blood cells.
  • LDH-3: Lungs.
  • LDH-4: Kidneys, pancreas, and placenta.
  • LDH-5: Liver and skeletal muscles.

What is it used for?

While a total LDH test shows that tissue damage exists, an LDH isoenzymes test helps pinpoint the location of that damage. It is used to diagnose or monitor conditions such as:

  • Anemia
  • Kidney or liver disease (including hepatitis and cirrhosis)
  • Pancreatitis
  • Pulmonary embolism (blood clot in the lung)
  • Muscular dystrophy
  • Certain cancers

Why do I need this test?

Your provider may order this test if you have symptoms of tissue damage, if a previous total LDH test showed elevated levels, or to monitor the progress of a known condition or the effectiveness of a treatment.

Test Procedure and Results

The test requires a simple blood draw from a vein in your arm. No special preparation is required. High levels of specific isoenzymes indicate damage to the corresponding tissues—for example, higher LDH-5 levels may suggest liver damage. However, elevated levels can also be caused by intense exercise, certain medications like aspirin, or the breakdown of red blood cells during the sample collection process. Always discuss your specific results with your health care provider.

Frequently Asked Questions

Intense physical exercise, such as heavy weightlifting or long-distance running, can temporarily elevate LDH-5 levels due to skeletal muscle stress, potentially mimicking liver or muscle disease. Certain medications, including high-dose aspirin, some antibiotics, and chemotherapy agents, can also raise LDH levels. Additionally, hemolysis, which is the breaking of red blood cells during the blood draw or sample handling, can artificially increase LDH-1 and LDH-2 levels, so it is critical to inform your provider about recent strenuous activity or medication changes before interpreting results.
The frequency of repeat testing depends on the specific condition and your provider's monitoring protocol. For acute conditions like hepatitis or a recent heart event, tests may be repeated daily or every few days to track the trajectory of recovery. For chronic conditions or cancer monitoring, tests are typically performed every few months or alongside other imaging and blood work to assess treatment effectiveness. Always follow the specific schedule provided by your healthcare team, as inconsistent timing can make it difficult to compare trends accurately.
standard total LDH test only indicates that tissue damage has occurred somewhere in the body but does not specify the location. The isoenzyme test separates the enzyme into its five specific forms (LDH-1 through LDH-5), allowing clinicians to pinpoint which organ or tissue is affected. For example, while both tests might show elevation in a patient with a heart attack, the isoenzyme test will specifically highlight increased LDH-1 and LDH-2 levels, confirming cardiac involvement rather than liver or muscle damage.
Not necessarily. While LDH-5 is most concentrated in the liver and skeletal muscles, elevated levels can result from conditions other than liver disease, such as muscular dystrophy, severe muscle injury, or intense exercise. Clinicians must correlate LDH-5 results with other liver function tests, such as ALT and AST, and evaluate clinical symptoms to determine if the elevation is due to hepatic damage or another cause. Isolated LDH-5 elevation without other liver enzyme abnormalities may point toward a muscular issue instead.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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