Lactate dehydrogenase (LDH)
An enzyme present in almost every cell that leaks out when cells are damaged or turn over rapidly. It is sensitive but non-specific — a raised LDH says 'something is breaking down' without saying where, so it is read alongside more specific tests.
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What it measures
LDH is an enzyme in the cytoplasm of virtually all tissues, involved in converting sugar to energy. Because it is everywhere, its release into blood is a general signal of cell damage or high cell turnover rather than a pointer to one organ. It rises in haemolysis (red cells breaking apart), tissue injury (heart, liver, muscle, lung), many cancers — especially lymphoma and germ-cell tumours where it also helps gauge bulk and monitor treatment — and in conditions with rapid cell turnover. It is a core part of the haemolysis panel (with haptoglobin, reticulocytes and bilirubin) and a prognostic marker in several cancers. A falsely high result can come simply from a blood sample that haemolysed in the tube.
What a high value can mean
- Haemolysis — red cells breaking down; LDH high with low haptoglobin, high reticulocytes and bilirubin.
- Sample haemolysis (artefact) — a common false cause from difficult venepuncture.
- Tissue injury — heart, liver, muscle, kidney, lung (e.g. pulmonary embolism, infarction).
- Cancer — lymphoma, leukaemia, germ-cell tumours; used for staging and monitoring.
- Infection / inflammation — including severe pneumonia.
- Megaloblastic anaemia (B12/folate deficiency) — very high from ineffective marrow turnover.
What a low value can mean
- Not clinically significant — a low LDH has no established disease meaning.
When to discuss with a doctor
LDH is almost never interpreted alone — its value is as part of a pattern. A high LDH with low haptoglobin and high reticulocytes points to haemolysis and prompts a cause hunt. In a known lymphoma or germ-cell tumour, LDH is tracked to gauge bulk and response. An isolated mildly raised LDH with no symptoms is often an artefact or non-specific and is repeated in context. Mediora.AI shows LDH alongside the haemolysis markers and flags the pattern rather than the number in isolation; deciding what a raised LDH means belongs with your doctor, who reads it with the rest of the picture.