Lactate Dehydrogenase
Metabolic PanelWhat is Lactate Dehydrogenase?
Lactate dehydrogenase (LDH) is a cytoplasmic enzyme found in virtually every living cell in the body. It catalyzes the reversible conversion of lactate to pyruvate with the concurrent interconversion of NADH and NAD+, a critical step in anaerobic glycolysis and gluconeogenesis. LDH exists as a tetramer composed of two subunit types—M (muscle) and H (heart)—which combine to form five distinct isoenzymes: LDH-1 (H4, predominant in heart and red blood cells), LDH-2 (H3M1, found in the reticuloendothelial system), LDH-3 (H2M2, found in lungs and other tissues), LDH-4 (HM3, found in kidneys and pancreas), and LDH-5 (M4, predominant in liver and skeletal muscle).
Because LDH is present in so many tissues, an elevated total LDH level is a nonspecific marker of cellular damage or death. When cells are injured or destroyed—whether from trauma, ischemia, hemolysis, or malignancy—LDH is released into the bloodstream. While a total LDH alone cannot pinpoint the source of tissue damage, isoenzyme fractionation or correlation with other biomarkers can help localize the affected organ. LDH is widely used in oncology to monitor tumor burden and treatment response, in hematology to assess hemolytic anemias, and as a prognostic marker in conditions ranging from lymphoma to COVID-19 pneumonia.
Why It Matters
LDH serves as a general sentinel for tissue damage throughout the body. Markedly elevated LDH is a hallmark of hemolytic anemia, megaloblastic anemia, widespread metastatic cancer, and lymphoma, where it correlates with tumor burden and prognosis. In oncology, LDH is incorporated into prognostic scoring systems such as the International Prognostic Index for lymphoma. Elevated LDH is also an important marker in Pneumocystis pneumonia, pulmonary embolism, and severe COVID-19, where it reflects lung tissue damage and predicts worse outcomes. Because of its ubiquity, LDH is most useful when interpreted alongside organ-specific markers.
Normal Reference Ranges
| Group | Range | Unit |
|---|---|---|
| Adults | 120–246 | U/L |
| Children (2–12 years) | 120–300 | U/L |
| Infants (0–2 years) | 180–430 | U/L |
| Newborns | 290–775 | U/L |
Reference ranges may vary by laboratory. Always compare results to the ranges provided by your testing facility.
What High LDH Levels Mean
Common Causes
- Hemolytic anemia (autoimmune, mechanical, or hereditary)
- Megaloblastic anemia (B12 or folate deficiency)
- Lymphoma, leukemia, or other malignancies
- Myocardial infarction
- Pulmonary embolism or infarction
- Liver disease (hepatitis, cirrhosis)
- Skeletal muscle damage or rhabdomyolysis
- Pneumocystis pneumonia or severe COVID-19
- Tissue ischemia or infarction of any organ
- In vitro hemolysis (spurious elevation from improper blood draw)
Possible Symptoms
- Symptoms depend on the underlying cause—LDH elevation alone does not produce symptoms
- Fatigue, jaundice, and dark urine if hemolysis is the cause
- Chest pain and shortness of breath with cardiac or pulmonary causes
- Night sweats, weight loss, and lymphadenopathy with lymphoma
- Muscle pain and weakness with rhabdomyolysis
What to do: An elevated LDH requires clinical correlation to identify the source. Your doctor may order LDH isoenzymes, a peripheral blood smear, haptoglobin, reticulocyte count, bilirubin, and liver enzymes to narrow the differential. If malignancy is suspected, imaging and further workup are indicated. Ensure the sample was not hemolyzed during collection, as this is a common cause of falsely elevated LDH. Repeat testing may be used to monitor disease activity or treatment response.
What Low LDH Levels Mean
Common Causes
- Genetic LDH deficiency (rare germline mutations in LDHA or LDHB)
- High intake of ascorbic acid (vitamin C), which can interfere with the assay
- Oxalate ingestion (rare)
Possible Symptoms
- LDH-A deficiency may cause exercise-induced myoglobinuria and muscle cramps
- LDH-B deficiency is typically asymptomatic
- Most individuals with low LDH have no symptoms
What to do: Low LDH is uncommon and usually clinically insignificant. If persistently low, consider genetic testing for LDH subunit deficiency, particularly if the patient experiences exercise-induced muscle symptoms. Rule out assay interference from high-dose vitamin C supplementation. No treatment is typically required.
When Is LDH Testing Recommended?
- When monitoring treatment response in lymphoma or other cancers
- When hemolytic anemia is suspected (along with haptoglobin and reticulocyte count)
- As part of the workup for unexplained tissue injury or organ damage
- In the evaluation of suspected Pneumocystis pneumonia or severe pneumonia
- When monitoring disease severity in hospitalized patients
Frequently Asked Questions
Related Biomarkers
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Upload Lab Results →Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Reference ranges may vary between laboratories. Always consult your healthcare provider for interpretation of your specific test results.