LDH (Lactate Dehydrogenase) Test

What is LDH?

Lactate dehydrogenase (LDH or LD) is an enzyme involved in converting lactate to pyruvate during energy metabolism. It is present in nearly all body tissues: heart, liver, kidney, muscle, lung and red blood cells. When cells are damaged, LDH leaks into the blood. Because it is non-specific (not tied to one organ), LDH is used as a general marker of tissue injury and cell turnover. LDH isoenzymes (LDH1-5) can sometimes identify which organ is involved.

LDH normal range

Causes of high LDH

LDH in cancer staging and monitoring

LDH is widely used in oncology as a prognostic marker. In testicular cancer, lymphoma, melanoma and lung cancer, a very high LDH correlates with higher tumour burden and poorer prognosis. It is included in staging systems for non-Hodgkin lymphoma (IPI score) and melanoma. Falling LDH during cancer treatment is a good sign; rising LDH during remission may indicate relapse.

Questions to ask your doctor

• Why is my LDH elevated?
• Do I need LDH isoenzyme testing to identify which organ is affected?
• Is this related to my anaemia, liver, or another cause?
• If being monitored for cancer, what LDH trend is expected?

Frequently Asked Questions

References

The clinical information on this page is drawn from peer-reviewed sources indexed by the US National Library of Medicine. Links go to the source so you can read it yourself.

1. Overview on Ordering and Evaluation of Laboratory Tests. In: StatPearls. Treasure Island (FL): StatPearls Publishing. NCBI Bookshelf NBK570615

References

Sources cited on this page. PubMed links open the original abstract.

1. Drent M, Cobben NA, Henderson RF, Wouters EF, van Dieijen-Visser M. Usefulness of lactate dehydrogenase and its isoenzymes as indicators of lung damage or inflammation. Eur Respir J. 1996;9(8):1736–1742. PMID 12756065 · doi:10.1183/09031936.96.09081736

Why LDH is elevated in so many conditions

Lactate dehydrogenase (LDH) is an intracellular enzyme found in virtually every tissue in the body – liver, heart, kidney, muscle, lung, and red blood cells. Its near-universal cellular distribution means that any condition causing cell death or damage – from any organ – can elevate serum LDH. This is why LDH is both a highly sensitive marker of tissue damage and a non-specific one: a high LDH raises the question "where is the tissue damage coming from?" rather than answering it.

LDH isoenzymes (LDH-1 through LDH-5) have organ-specific distributions – LDH-1 and LDH-2 are highest in the heart and red blood cells; LDH-5 is predominant in the liver and muscle. Isoenzyme patterns historically differentiated MI from liver damage, but cardiac troponin has replaced LDH for cardiac diagnosis. LDH isoenzyme testing retains a niche role in specific situations (neonatal haemolysis, confirming Duchenne muscular dystrophy origin of elevated LDH).

Clinical applications where LDH has diagnostic value

• Haemolysis: When red blood cells rupture, LDH-1 and LDH-2 are released – often with high LDH (10–50× normal in severe haemolysis). LDH is one of the "haemolysis triad": raised LDH + raised bilirubin (from haemoglobin breakdown) + reduced haptoglobin (consumed by free haemoglobin). Together, these confirm intravascular or extravascular haemolysis.
• Lymphoma and haematological malignancies: Tumour lysis (spontaneous or from chemotherapy) releases LDH from lymphoma cells. The pretreatment LDH level is an integral component of prognostic scoring systems – the International Prognostic Index (IPI) for diffuse large B-cell lymphoma includes LDH as one of five factors. A very high LDH (above twice normal) in a patient with lymphoma indicates high tumour burden and poor prognosis.
• Tumour lysis syndrome (TLS): After chemotherapy for highly proliferative cancers (acute leukaemia, Burkitt lymphoma), massive tumour cell death releases intracellular contents: uric acid, potassium, phosphate, and LDH all rise dramatically. Cairo-Bishop criteria for TLS require LDH above twice the upper limit of normal.
• COVID-19 and critical illness: LDH became a widely used severity marker in COVID-19 – elevated LDH (above 300 IU/L) was associated with increased risk of mechanical ventilation and mortality. LDH similarly reflects severity in sepsis, ARDS, and other critical illnesses.
• Testicular cancer monitoring: LDH is one of three tumour markers (alongside AFP and beta-hCG) used in the staging and monitoring of non-seminomatous germ cell tumours. Elevated LDH with normal AFP and beta-hCG occurs in seminoma.