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.
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.