LDH (lactate dehydrogenase)

LDH (lactate dehydrogenase) is an enzyme in almost all body cells, entering blood when cells are damaged or break down. Raised LDH is therefore a general sign of tissue damage: it does not identify the affected organ but helps a doctor investigate anaemia, liver disease and some malignancies and monitor treatment.

Who the test is for

• people with suspected increased red blood cell breakdown (haemolysis), alongside a blood count, reticulocytes and bilirubin;
• people with suspected liver disease, alongside AST, ALT and GGT;
• people with muscle damage, alongside CK (creatine kinase);
• patients with lymphoma, leukaemia, melanoma or a germ cell tumour, for investigation and monitoring;
• people having a general or sports health examination.

What LDH is and what it shows

LDH participates in converting sugar into energy within cells. It is most abundant in the liver, muscles, heart, kidneys, lungs and red blood cells. Damage to cells in any of these tissues raises blood LDH.

LDH is therefore non-specific: an elevated result indicates cell damage somewhere in the body but not where. A doctor always interprets it alongside other tests, such as a blood count, liver enzymes or creatine kinase.

LDH and heart attacks

LDH was previously used to confirm heart attacks, but this is now outdated. A heart attack is established using troponin, specific to heart muscle, alongside ECG and examination in an emergency department. Chest pain, particularly with difficulty breathing, sweating or nausea, requires emergency medical assistance, not a self-selected laboratory test. We explain the tests now used for the heart in the article on cardiac biomarkers.

LDH in malignancies

LDH is not a test to detect cancer and is not used to screen healthy people. In already diagnosed malignancies it helps assess disease extent and treatment response. In germ cell tumours, such as testicular tumours, it is measured together with AFP and beta HCG, before and after surgery and during monitoring. In lymphoma and melanoma it contributes to assessment of disease extent and prognosis. The purpose of tumour markers, in a separate article.

Preparation and sample

LDH is measured in venous blood and fasting is unnecessary. Avoid exhausting training for a day or two before collection because intense exertion temporarily raises muscle LDH. Mention recent injury or surgery during collection.

Red blood cells contain much LDH, so their breakdown in the sample after collection (sample haemolysis) falsely raises results. If the sample is haemolysed, collection is repeated.

How to interpret the result

LDH is expressed in U/L (units per litre). The reference interval depends on age and method and is printed on the report; children have higher values than adults. A doctor interprets results alongside symptoms and other tests.

• Raised LDH may accompany haemolytic anaemia, anaemia due to deficiency of vitamin B12, hepatitis and other liver diseases, infectious mononucleosis, muscle damage, pneumonia, kidney disease and some malignancies. Mildly raised LDH with otherwise normal findings is often temporary, for example after exertion, so a doctor may repeat testing.
• Low LDH is rare and generally not clinically significant.

How to arrange testing

You can have blood taken without an appointment or referral at one of our branches across Croatia (listed under Contact). Prices for all tests and panels are available in the service price list. When investigating a liver cause of raised LDH, it is usually measured alongside the Liver health panel (AST, ALT, GGT).

Frequently asked questions

What does raised blood LDH mean?

Raised LDH means cells somewhere in the body are being damaged or breaking down, but does not say where or why. The cause may be harmless, such as intense training or sample haemolysis, but may also be blood, liver, muscle or lung disease. A doctor decides whether to repeat or expand testing based on symptoms and other findings.

Is LDH a tumour marker?

Not as a test for detecting cancer. In people with known lymphoma, melanoma or a germ cell tumour, LDH helps assess disease extent and monitor treatment, but raised LDH alone does not indicate a tumour.

Can training raise LDH?

Yes. Prolonged or very strenuous training temporarily raises LDH and often CK. If results are mildly raised after exertion, a doctor usually recommends repeating them after several days of rest.

Which tests are performed alongside LDH?

It depends on the reason. For suspected red blood cell breakdown they include blood count, reticulocytes and bilirubin; for liver disease, liver enzymes; and for muscle damage, CK. In germ cell tumours, LDH is monitored with AFP and beta HCG.