LDH blood test: what the result means

Lactate dehydrogenase (LDH) is an enzyme that takes part in turning glucose into energy and is present in almost every cell in the body — in the heart, the liver, the kidneys, the muscles, the lungs, the blood cells and the brain. When cells are damaged or die because of illness, infection, injury or another cause, LDH is released into the blood and the amount in the blood rises. That is why the LDH test is not a test of one particular organ — it shows tissue damage in general, and to establish the cause further tests are most often needed (for example liver markers such as ALT, as well as troponin, a full blood count with a white cell differential or imaging tests). LDH is sometimes also measured in other fluids, for example pleural or abdominal fluid, to assess where that fluid comes from. Because LDH is a non-specific marker, it is most often assessed together with clinical symptoms and other tests rather than on its own.

• When tissue or organ damage is suspected — for example after an injury, intense muscle overload or surgery
• When looking into the cause of anaemia — LDH helps to tell haemolytic anaemia apart from other kinds of anaemia
• When monitoring liver disease, together with the liver enzymes (ALT, AST, bilirubin)
• When assessing certain cancers — leukaemia, lymphoma or other tumours, where LDH is used to follow how the disease develops
• When infectious mononucleosis or another infection causing tissue damage is suspected
• When there are unclear symptoms — tiredness, weakness, breathlessness — and the doctor wants to check the general condition of the tissues

A raised LDH does not always mean a serious illness — it rises with intense exercise or with some medicines. But a markedly raised LDH can point to tissue damage: a heart attack, haemolytic anaemia, liver disease, a muscle injury or an infection. To establish the cause, a doctor assesses LDH together with other tests and with symptoms.

• Intense physical activity
• Some medicines, among them aspirin
• A heart attack or other tissue damage caused by reduced blood flow
• Haemolytic anaemia — the breakdown of red blood cells
• Infectious mononucleosis or another severe infection
• Leukaemia, lymphoma or other cancers
• Liver disease
• A muscle injury or muscular dystrophy
• Inflammation of the pancreas (pancreatitis)
• A stroke or other death of tissue

What to discuss with a doctor

• Whether there was intense physical activity before the test, or medicines being taken that could affect the result
• Further tests to establish the cause — liver markers, troponin, a full blood count
• Symptoms — tiredness, pain, breathlessness — which help to link the result with a possible cause
• When to repeat the test, so that the change over time can be seen

A low LDH occurs less often than a raised one. It can be linked to large doses of vitamin C or vitamin E, or to a rare inherited condition — lactate dehydrogenase deficiency. The clinical significance of a low LDH is usually smaller than that of a raised one, so the result is worth discussing with a doctor alongside your general state of health.

• Taking large doses of vitamin C or vitamin E
• A rare inherited lactate dehydrogenase deficiency

What is looked at with a low LDH

• Whether vitamin supplements are being taken in large doses
• Family history of rare inherited enzyme disorders, if the reduction is persistent

Related tests

• ALT
• AST
• Bilirubin
• Troponin
• Creatine kinase
• Haemoglobin