The Lactate Dehydrogenase (LDH) test is a blood test that measures the level of an enzyme called lactate dehydrogenase. LDH is found in many tissues throughout the body, including the heart, liver, kidneys, lungs, muscles, blood cells, and brain. Because LDH is present in so many places, it is considered a non-specific marker of tissue damage.

When cells are injured or destroyed, LDH can leak into the bloodstream. As a result, higher LDH levels may indicate that there is tissue damage, inflammation, or rapid cell turnover occurring somewhere in the body. A single LDH result typically cannot pinpoint the exact organ involved, so clinicians usually interpret LDH along with your symptoms, physical exam, and other lab tests (such as liver enzymes, kidney function tests, complete blood count, bilirubin, or cardiac markers).

In plain language: LDH is a “signal” that cells may be under stress or being damaged. Mild elevations can occur for many reasons, while more significant increases may suggest more extensive injury, disease activity, or (in some cases) cancer-related cell breakdown. Normal LDH levels make significant widespread tissue breakdown less likely, but they do not rule out all disease.

Important note: LDH can be falsely elevated if the blood sample is hemolyzed (red blood cells break during or after the blood draw). If your result is unexpectedly high, your provider may repeat the test or check related labs to confirm.

Doctors order an LDH blood test when they suspect tissue injury or want to monitor conditions that can cause ongoing cell damage. It may be used as a screening or follow-up test when symptoms or other labs suggest inflammation, organ stress, or blood cell breakdown.

Common reasons your clinician may request LDH include:

Possible tissue damage or inflammation—especially when symptoms are non-specific, such as:

Fatigue, weakness, unexplained fever, body aches, or general malaise; unexplained pain (such as chest or abdominal pain) when broader testing is being done to find a cause.

Evaluation of hemolysis (breakdown of red blood cells), which may be suspected with symptoms or findings such as:

Jaundice (yellowing of skin/eyes), dark urine, anemia, shortness of breath, rapid heartbeat, or abnormal results on a complete blood count (CBC). LDH is often interpreted alongside haptoglobin, bilirubin, and a reticulocyte count.

Assessment of organ-related conditions, since LDH may rise with injury to organs such as the liver, lungs, or muscles. Your provider may order LDH as part of a broader panel when they are investigating abnormal liver tests, muscle pain/weakness, or suspected lung inflammation.

Monitoring certain cancers and their response to treatment. In some cancers (including lymphomas and germ cell tumors), LDH can reflect tumor burden or aggressive disease activity. It may also be used as a general marker of treatment response when tracked over time.

Following disease activity over time. Sometimes the trend matters more than a single result—rising LDH can suggest worsening cell injury, while falling LDH can indicate recovery or improvement with treatment.

• Hemolytic anemia (including autoimmune hemolytic anemia)
• Hepatitis and other liver diseases (including cirrhosis or liver injury)
• Muscle injury and muscle diseases (including rhabdomyolysis)
• Myocardial infarction (heart attack) and other cardiac injury (historically used; now often supplemented/replaced by troponin testing)
• Pulmonary embolism and some lung diseases causing tissue strain or damage
• Kidney disease or kidney infarction (less common, but can raise LDH)
• Severe infections or sepsis
• Mononucleosis and other viral illnesses that cause widespread inflammation
• Cancers with high cell turnover (e.g., lymphoma, leukemia, testicular/germ cell tumors)
• Tumor lysis syndrome (rapid breakdown of cancer cells, often after treatment)

• Identifying or monitoring tissue damage when symptoms are unclear (a broad “cell injury” marker)
• Supporting evaluation and follow-up of anemia and suspected hemolysis
• Monitoring cancer activity and response to treatment in selected cancers where LDH is clinically useful
• Tracking recovery after significant illness, inflammation, or injury by following LDH trends over time
• Helping assess possible liver or muscle injury as part of broader lab monitoring