LDH
Lactate Dehydrogenase
What this test measures
LDH is an enzyme found in almost all body tissues. When cells are damaged, they release LDH into the blood. It's a general marker of tissue damage.
Understanding the numbers
Typical range: 140-280 U/L (may vary by lab)
LDH is not specific to any one organ. Raised levels tell us there's cell damage somewhere, but not where.
- Normal: 100–280 U/L
- Mildly raised: 280–500 U/L
- Moderately raised: 500–1000 U/L
- Markedly raised: 1000–1500 U/L
Key numbers
- 280 U/L — Typical upper limit
- 1000 U/L — Markedly raised — investigate urgently
Reference range varies by laboratory method. LDH is non-specific — it rises in tissue injury anywhere: haemolysis, ischaemia, infections, lymphoma. It is mainly used as part of specific pathway workups (e.g. lymphoma staging, haemolysis, PCP pneumonia) rather than as a stand-alone test.
Ranges can vary slightly between laboratories — your report may show slightly different numbers. This page does not read or interpret your result; your GP looks at it alongside your history and other tests.
What a higher-than-normal result can mean
- Indicates cell or tissue damage somewhere in the body
- Can be raised by heart attack, liver disease, or muscle injury
- Anaemia (when red blood cells break down) raises LDH
- Some cancers and infections can cause elevated LDH
Questions you could ask your GP
- What might be causing my raised LDH?
- Do I need more specific tests to find the source?
- Is this related to any condition I already have?
- Will I need repeat testing to monitor this?
Example stories
These are made-up examples to show how results are talked about in real appointments. They are not real patients.
High LDH — lymphoma staging
Vikram presented with enlarged neck lymph nodes and night sweats. LDH 680, confirmed lymphoma on biopsy.
What the GP said: “The LDH level helps us understand how active your disease is — the higher it is, the higher the disease burden. It also helps us track response to treatment.”
What happened next: After four cycles of chemotherapy, his LDH had dropped to 220 — a treatment response marker.
In lymphoma and some leukaemias, LDH is a useful 'disease activity' marker — tracking it alongside imaging gives a fuller picture of treatment response.
Raised LDH — haemolytic anaemia
Aziz was tired and yellow with a low haemoglobin of 88. LDH was 520, reticulocytes high, bilirubin 48, Coombs positive.
What the GP said: “Your red blood cells are being destroyed faster than normal — autoimmune haemolytic anaemia. The LDH comes from the breaking cells. Steroids should control it.”
What happened next: Aziz responded to steroids; his LDH came down to 250 and haemoglobin recovered.
In haemolysis, LDH rises together with indirect bilirubin and reticulocytes — all three point to red cells being broken down. LDH is one piece of the picture, not the diagnosis on its own.
LDH in suspected pulmonary embolism
Jeanette had sudden breathlessness. D-dimer was high, LDH 340, CT confirmed pulmonary embolism.
What the GP said: “LDH isn't a diagnostic test for PE, but a rise can happen when part of the lung tissue is starved of blood. We start anticoagulation — that's the main treatment.”
What happened next: With apixaban her breathlessness improved; LDH normalised over two weeks.
Mild LDH rises in acute illness are non-specific. The diagnostic work is done by D-dimer, scans and the clinical picture — LDH is a bystander rather than the lead actor.
HIV and PCP pneumonia
Tim had dry cough and breathlessness on exertion. LDH 710, oxygen 90% on air. HIV test positive; PCP (Pneumocystis) on bronchoscopy.
What the GP said: “A high LDH with progressive breathlessness and a positive HIV test raised our suspicion of PCP — that's a specific lung infection we can treat.”
What happened next: Tim was treated with co-trimoxazole and steroids, started antiretrovirals, and recovered fully.
In specific clinical contexts — especially HIV — a raised LDH with breathlessness points to PCP pneumonia. Context turns a non-specific test into a useful clue.
Before you act on anything here
This page is general information, written to help you understand — it is not personal medical advice and it cannot tell you what is right for you. Talk to your own GP, pharmacist or nurse about your own health.
- Need help now but it's not an emergency? Call NHS 111 or use 111.nhs.uk.
- Emergency? Call 999 or go to A&E.