What this test measures
Lactate dehydrogenase is an enzyme found in nearly every cell of the body — heart, liver, kidney, muscle, red blood cells, brain, lung and many tumours. It interconverts pyruvate and lactate during energy metabolism. When cells die or are damaged, LDH leaks into blood.
Labs measure total serum LDH; in selected cases, the five LDH isoenzymes (LDH-1 through LDH-5) can be fractionated to identify the tissue source — LDH-1/2 are heart and red cells, LDH-3 is lung, LDH-4/5 are liver and skeletal muscle.
Why it matters
LDH is a workhorse "something is dying" marker. In India, it is most commonly used to monitor haematological disease (haemolytic anaemias, lymphoma, leukaemia, multiple myeloma — where it reflects tumour burden and is part of the International Prognostic Index), to support a diagnosis of haemolysis, to track megaloblastic anaemia, and to evaluate exudative vs transudative pleural effusions (Light's criteria).
It is also used in liver and muscle injury, COVID-19 severity prediction, ischaemic conditions (mesenteric ischaemia, large emboli), and as a tumour marker in germ cell tumours and metastatic disease. The test is cheap and widely available — but never diagnostic on its own.
How to prepare
No fasting required. Avoid heavy exercise in the 24 hours before — strenuous activity can transiently raise LDH from muscle. The sample must be handled gently — haemolysis during venipuncture causes spuriously high LDH (red cells contain massive amounts).
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Lactate Dehydrogenase (LDH) (U/L)[1][2] | 140 – 280 (method-dependent) | Low LDH is uncommon and rarely concerning. Can be seen with high-dose vitamin C, hypothyroidism, or genetic LDH deficiency (rare). | Mild rise (1–2×) — many causes including muscle exertion, mild haemolysis, viral infections, fatty liver. Moderate rise (2–5×) — haemolysis, megaloblastic anaemia, lymphoma, hepatitis, recent MI, mesenteric ischaemia. Marked rise (>5×) — massive haemolysis, lymphoma / leukaemia, tumour lysis syndrome, severe ischaemic injury, fulminant hepatitis. LDH should always be interpreted in context — sample haemolysis is the most common reason for an unexpectedly high value. |
Common clinical uses of LDH
| Setting | What LDH tells you | Associated markers |
|---|---|---|
| Haemolysis | LDH rises with red cell breakdown | Low haptoglobin, raised indirect bilirubin, raised reticulocytes |
| Lymphoma / leukaemia | Reflects tumour burden, prognostic marker in IPI score | CBC, peripheral smear, imaging |
| Megaloblastic anaemia (B-12 / folate deficiency) | Often markedly raised due to ineffective erythropoiesis | MCV, B-12, folate, peripheral smear |
| Pleural effusion (Light's criteria) | Pleural fluid LDH/serum LDH > 0.6 = exudate | Pleural protein, glucose, cytology |
| Tumour lysis syndrome | Massively raised after chemotherapy starts | Uric acid, potassium, phosphate, calcium |
| Acute MI (historical) | LDH rises 24–48 hours after — replaced by troponin | Troponin I/T, CK-MB |
Frequently asked questions
My LDH is mildly raised. What does that mean?
LDH is non-specific — many things raise it. The most common reasons for mild rises are sample haemolysis during collection, recent strenuous exercise, viral illness, mild liver disease, or early haematological disease. Your doctor will look at the rest of the picture (CBC, smear, LFT) before pursuing causes.
Do I need to fast?
No. But avoid heavy exercise for 24 hours before — muscle damage raises LDH.
Can a haemolysed sample give a wrong LDH?
Yes — this is the single most common reason for a "high" LDH that does not match the patient. Red blood cells are packed with LDH. If the sample is haemolysed (looks pink), the lab usually flags it and you should re-test.
Why is LDH used in lymphoma?
In Hodgkin and non-Hodgkin lymphoma, LDH reflects tumour cell turnover and is part of standard prognostic scores (International Prognostic Index for diffuse large B-cell lymphoma). Rising LDH during treatment can signal poor response.
Is LDH still used for heart attack diagnosis?
No. Troponin replaced LDH for diagnosing myocardial infarction in the 1990s — troponin is more specific and rises earlier. LDH is largely of historical interest in cardiac diagnosis.
How is LDH used in pleural effusion?
Light's criteria use the ratio of pleural fluid LDH to serum LDH (and protein) to separate exudates (infection, malignancy, autoimmune) from transudates (heart failure, cirrhosis, low albumin). Pleural LDH > 0.6 of serum LDH points to an exudate.
Can LDH be raised in COVID-19?
Yes — LDH was used during the pandemic as part of severity scoring; markedly raised LDH (>500–600) correlated with worse outcomes from lung injury, but is not specific to COVID-19.
Related Liver / Enzymes tests
Tests commonly ordered alongside LACTATE DEHYDROGENASE (LDH), or that help interpret an unexpected result.
Sources & references
- NIH MedlinePlus — LDH Test · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Lactate Dehydrogenase · accessed 2026-05-30T00:00:00.000Z
- Mayo Clinic Laboratories — Lactate Dehydrogenase, Serum · accessed 2026-05-30T00:00:00.000Z
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