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
| Group | Normal Range (U/L) |
|---|---|
| Adults | 140 – 280 U/L (varies slightly by lab) |
| Children | Higher than adults (normally elevated) |
Causes of high LDH
| Cause | How high LDH rises | Notes |
|---|---|---|
| Haemolysis (red cell breakdown) | Very high | LDH1 dominant; check haptoglobin |
| Liver disease | Moderately high | LDH5 dominant; use with LFT |
| Heart attack (MI) | High (historic use) | Troponin now preferred |
| Pulmonary embolism | Mild-moderate | Non-specific |
| Lymphoma / leukaemia | Very high | Very high LDH = aggressive tumour |
| Anaemia (megaloblastic) | High | B12/folate deficiency with ineffective erythropoiesis |
| Muscle injury / rhabdomyolysis | Very high | CK also very high |
| Kidney infarction | High | LDH5 |
| COVID-19 / severe infections | Elevated | Marker of tissue damage severity |
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?