The Lactate Dehydrogenase (LDH) test is a fundamental diagnostic tool widely used in modern medicine to evaluate tissue health, identify disease progression, and monitor a variety of acute and chronic medical conditions. As non-specific but responsive markers of cell damage, LDH levels offer valuable clues about what’s happening inside the body even when symptoms alone are unclear.

What is the LDH Test?

Lactate Dehydrogenase (LDH) Enzymes are found in almost all the cells in our body, including the heart, liver, kidneys, muscles, brain, lungs, and red blood cells. Biologically, it has the role of catalyzing the transformation of lactate (which is a product of glucose metabolism) into pyruvate, an essential step in the process of cellular energy production.

When cells break down or the tissues get damaged, LDH is released from the affected cells into the blood or in other fluids depending on the damage occurring in other sites. An LDH blood test is therefore an indication of the rate of LDH enzyme in the bloodstream and gives a corresponding indication that your cell is injured or has increased cellular turnover.

Why Is an LDH Test Done?

The Lactate Dehydrogenase (LDH) test is primarily used as a marker of tissue damage. As LDH is present in many tissue types, the test is used as a general indicator of cell injury, rather than pinpointing one single disease.

Key Uses of the LDH Test

• Detection of tissue damage: An increase in the level of LDH can be found in any significant injury or disease process which will lead to damage of the heart, liver, muscles, lungs, kidneys or the blood cells.
• The test helps diagnosing and monitoring diseases such as:
• Liver diseases such as hepatitis or cirrhosis
• Kidney disorders
• Cardiovascular diseases, such as the diagnosis and monitoring of heart attack (now mostly substituted by other examinations)
• Blood diseases such as hemolytic anemia or leukemia
• Muscle diseases or injuries like muscular dystrophy or rhabdomyolysis
• Specific types of cancers, in particular, lymphoma, leukemia, testicular cancer and melanoma
• Severe infections (e.g., sepsis, encephalitis)
• Monitoring of the disease: Normal or increased LDH levels may indicate the extent and severity of a chronic illness or the effectiveness of active ongoing treatment (e.g., cancer), or the response to infection).

Test Procedure: How Is LDH Measured?

Sample Collection

• LDH testing requires a simple blood draw, usually from a vein in your arm.
• In some cases (e.g., when evaluating fluid collections like pleural or peritoneal effusions), LDH can also be measured in body fluids.

Preparation

• There is no special preparation you do not need to fast for an LDH blood test.

Risks

• The risks are minimal and similar to other blood draws: potential mild pain, bruising, or slight bleeding at the site.

Understanding LDH Test Results

Your blood sample is tested and analyzed in a laboratory using automated enzymatic assays. Results are usually given in international units per liter (IU/L), with slight variations in ranges depending on methodology and demographics.

Normal Range

• Reference ranges can vary slightly by laboratory. Always interpret values based on the normal range provided in your test report.
• Children and certain laboratories may have slightly different normative values.

Table: LDH Levels and Clinical Interpretation

High LDH: What Does It Mean?

Elevated LDH is a sign of tissue injury or increased cell turnover. The test is not disease-specific and must be interpreted alongside your medical history, symptoms, and other laboratory or imaging studies.

Common causes of high LDH include:

• Heart attack (myocardial infarction)
• Hemolytic anemia (destruction of red cell overproduction)
• Liver disease (e.g., viral hepatitis, cirrhosis, etc.)
• Muscle dysfunction,injuries or muscular dystrophy
• Kidney disease
• The infectious disease (e.g., mononucleosis, sepsis).
• The malignancies of the blood like leukemia or lymphoma
• Cerebral (advanced) cancer or lysis of tumors
• Pancreatitis
• Stroke, severe trauma, or tissue damage
• Low blood pressure and hypoxia (impaired oxygenation)

Additional tests (including LDH isoenzyme analysis, organ-specific markers, or imaging) will generally be needed to find out what exactly has caused the elevated LDH.

Low LDH: Clinical Significance

Low LDH is uncommon and does not often require clinical attention. On rare occasions, it may be linked to certain hereditary deficiency of enzymes, but on most occasions, there could be laboratory error. For most patients, a low LDH value does not warrant medical concern.

LDH Isoenzymes: A Step Further

LDH exists in five isoenzyme forms (LDH-1 to LDH-5), each more prevalent in specific tissues:

Testing for these isoenzymes is rarely needed now but may be used if your doctor wants to identify which organ system caused the LDH rise.

For example, a predominance of LDH-1 may suggest heart muscle injury, while LDH-5 is elevated in liver or muscle disease.

When Is an LDH Test Recommended?

Your doctor may order an LDH test if you have:

• Symptoms suggestive of tissue damage (e.g., unexplained fatigue, weakness, jaundice, anemia, or muscle pain)
• Chronic diseases (e.g., leukemia, lymphoma, liver or kidney disease) to review progression or treatment response
• Acute illnesses (e.g., heart attack, severe infection, unexplained fluid buildup)
• Unexplained abnormal results from other blood tests (e.g., anemia or high liver enzymes)
• Suspected tissue injury after trauma, surgery, or medication reactions.

Comparative Note: LDH vs. PCT (Procalcitonin) Test

While the LDH test is a general marker of cell damage or disease in the body, the procalcitonin (PCT) test is specifically used to distinguish bacterial infections—especially sepsis—from other causes of inflammation. Both are valuable in different ways:

Refer to your healthcare provider for the test best suited to your clinical scenario.

Factors Influencing LDH Test Results

Interpretation of LDH levels must consider:

• Recent vigorous exercise (may increase muscle LDH)
• Hemolysis during blood collection (false elevation due to red cell rupture in the tube)
• Medications that affect the liver or kidneys
• Advanced age or pregnancy (normal variations)

Always share your full medical and medication history during laboratory evaluation.

Summary Table: LDH Test Key Facts

Conclusion

LDH test is a powerful, non-specific radio test of tissue injury. It has a broad utility ranging from infection and heart disease to liver injury and cancer monitoring but its lack of specificity and thus must be interpreted by using other clinical data and diagnostic findings.

In case you obtain the abnormal results of LDH, discuss with your healthcare provider whether you should perform repeated analysis or the rechecks. Bear in mind that individuals with elevated (or low) value rarely provide diagnosis in themselves, it is important to remember the context and history of the individual, as well as consider the context of the readings and anything that would affect it, and full analysis.