Lactate Dehydrogenase (LDH) Test
The Lactate Dehydrogenase (LDH) test measures a ubiquitous intracellular enzyme released when cells are damaged or turnover increases, providing a sensitive but non-specific marker of tissue injury. It supports assessment of haemolysis and thrombotic microangiopathy and has a prognostic role in lymphoma, germ cell tumours, and advanced melanoma.
1
Biomarkers
Blood (serum)
Sample
1–3 business days
Turnaround
No
Fasting
What is the LDH test?
The Lactate Dehydrogenase Test measures serum LDH, a ubiquitous intracellular enzyme released into the circulation when cells are damaged or turnover increases. As a marker present in nearly all tissues, it provides a sensitive but non-specific signal of cellular injury across many organ systems. In the diagnostic landscape, LDH is used as a supportive marker rather than a specific diagnostic test. It is valuable in assessing haemolysis, where it rises with red cell breakdown, and in thrombotic microangiopathies such as thrombotic thrombocytopenic purpura. It has a defined prognostic role in oncology — contributing to risk stratification in lymphoma, staging of germ cell tumours, and assessment of advanced melanoma — and rises markedly in conditions of rapid cell turnover such as tumour lysis and megaloblastic anaemia. Because elevation is non-specific, LDH is interpreted alongside the clinical picture and more targeted tests, and isoenzyme fractionation is occasionally used to suggest the tissue source. Careful specimen handling is essential, as in vitro haemolysis falsely raises the result.
What does the LDH test measure?
Lactate dehydrogenase is a cytoplasmic enzyme present in virtually all body tissues that catalyses the reversible interconversion of lactate and pyruvate, a key step in anaerobic energy metabolism. It exists as five isoenzymes (LDH-1 to LDH-5) with characteristic tissue distributions across heart, red cells, kidney, liver, muscle, and lung. Because it is ubiquitous and released when cells are damaged, serum LDH rises with cellular injury or increased turnover in many tissues.
LDH is a sensitive but highly non-specific marker of tissue damage or increased cell turnover, used to support assessment of haemolysis, tissue injury, and certain malignancies. It has an established prognostic role in some cancers — lymphoma, germ cell tumours, and advanced melanoma — and is a useful marker in haemolytic anaemias and conditions such as thrombotic microangiopathy. Because so many processes raise it, an elevated LDH localises poorly and requires interpretation with the clinical context and more specific tests.
Why is the LDH test ordered?
- Assessment of suspected haemolysis or haemolytic anaemia, where LDH rises with red cell breakdown alongside markers such as haptoglobin and bilirubin
- Risk stratification and monitoring in lymphoma, where LDH contributes to prognostic indices
- Staging and monitoring of germ cell tumours, where LDH is an established tumour marker alongside AFP and beta-hCG
- Assessment of advanced melanoma, where LDH informs prognosis in metastatic disease
- Investigation of suspected thrombotic microangiopathy (e.g. thrombotic thrombocytopenic purpura), where LDH is markedly elevated
- Evaluation of suspected tumour lysis syndrome or conditions of rapid cell turnover
- Support for the assessment of tissue injury — including hepatic, muscle, or pulmonary causes — within a broader workup
- Investigation of markedly raised LDH in suspected megaloblastic anaemia, where ineffective erythropoiesis produces high levels
Sample collection and turnaround
Sample type
Blood (serum)
Fasting required
No
Collection method
Venipuncture at patient service centre
Turnaround
1–3 business days
Collection notes
Atraumatic collection and prompt serum separation are essential, as in vitro haemolysis and delayed separation falsely raise LDH. Avoid vigorous exercise before collection, which can elevate the result. Note recent tissue injury or surgery. # REVIEWER FLAG: Confirm Access Medical Laboratories tube type, handling, and haemolysis-rejection criteria before publication.
Specimen requirements
Minimum 0.5 mL serum. Separate serum from cells promptly; avoid haemolysed specimens.
What can affect LDH results?
Red cells are rich in LDH, so haemolysis during collection or processing releases LDH into serum and falsely raises the result. This is the single most important pre-analytical pitfall, requiring careful, atraumatic collection and prompt separation.
Prolonged contact with cells before separation allows continued LDH leakage, artefactually raising the measured level. Timely processing is essential.
Skeletal muscle is rich in LDH, so vigorous exertion, trauma, or intramuscular injury raises serum LDH independent of other pathology.
Damage to any LDH-rich tissue — including hepatic, cardiac, pulmonary, or renal — releases the enzyme, contributing to non-specific elevation.
Platelets contain LDH, so platelet-rich or poorly processed samples can give higher values; serum and plasma handling must follow protocol. # REVIEWER FLAG: Confirm Access Medical Laboratories sample type and handling.
LDH activity measurement is temperature- and method-dependent, so reference ranges and results are not directly comparable across laboratories and assays.
What do LDH results mean?
Elevated
A raised LDH indicates tissue damage or increased cell turnover but localises poorly given its ubiquity. Very high levels suggest haemolysis, tumour lysis, megaloblastic anaemia, or extensive tissue injury, while moderate elevation accompanies many conditions. In oncology it carries prognostic weight in lymphoma, germ cell tumours, and melanoma. Always exclude in vitro haemolysis as an artefactual cause before clinical interpretation.
Normal
A normal LDH makes significant active haemolysis or large-scale tissue injury less likely at the time of testing but does not exclude localised or early pathology. It is interpreted with the clinical context and more specific markers.
Reduced
A low LDH is uncommon and of little clinical significance, occasionally associated with certain genetic enzyme variants. It generally requires no action.
Note: LDH is highly non-specific and cannot identify the source of tissue damage on its own, so it is always interpreted with the clinical picture and targeted tests; isoenzyme fractionation may suggest a tissue origin. In vitro haemolysis is a frequent cause of artefactual elevation and must be excluded. Reference ranges are method- and temperature-dependent, so serial results should use the same laboratory and assay.
Frequently asked questions
It measures lactate dehydrogenase, a ubiquitous intracellular enzyme released into the blood when cells are damaged or turnover increases. It is a sensitive but non-specific marker of tissue injury across many organ systems.
How to access the LDH test
The LDH reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.
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Published: June 3, 2026
Last reviewed: June 3, 2026
- Farhana A, Lappin SL. Biochemistry, Lactate Dehydrogenase. StatPearls. (2023)
- Barranco-Lampón G, et al. Lactate dehydrogenase as a prognostic factor. (representative oncology reference) (2020)
- Zaninetti C, et al. Diagnosis and treatment of thrombotic thrombocytopenic purpura. Haematologica. (2019)
- Barth DA, et al. Prognostic value of LDH in cancer. (representative reference) (2020)
This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.
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