Lactate dehydrogenase (LDH) is an enzyme found in cells throughout the body, including the liver, heart, kidneys, skeletal muscle, red blood cells, and lungs. When cells are damaged or destroyed, LDH is released into the bloodstream. An elevated LDH indicates that tissue damage is occurring somewhere, but the test alone does not tell you which organ is responsible.
This non-specificity is both the limitation and the value of LDH. It serves as a broad screening marker for cell damage across multiple organ systems, and it is typically used alongside more targeted tests to build a clinical picture. For example, elevated LDH in combination with abnormal liver enzymes points toward liver involvement, while elevated LDH with low haptoglobin and high reticulocytes suggests haemolysis (red blood cell destruction).
LDH is widely used in oncology as a prognostic marker. In lymphoma, leukaemia, testicular cancer, and melanoma, rising LDH can indicate disease progression or inadequate treatment response. In haematology, it helps confirm haemolytic processes. In cardiology and respiratory medicine, it contributes to the assessment of myocardial infarction and pulmonary embolism, though more specific markers like troponin have largely taken over the cardiac role.
Vigorous exercise and haemolysis of the blood sample during collection can both raise LDH artificially. It is important to avoid strenuous physical activity for at least 24 hours before the test. If your result is unexpectedly elevated, your practitioner may check whether sample handling could have affected the measurement.
LDH is best understood as a starting point. An abnormal result prompts further investigation to identify the source. Your practitioner will use the pattern of other results, your symptoms, and clinical context to determine the next steps.
To detect tissue damage from any cause, investigate haemolysis, support the assessment of liver disease, monitor certain haematological conditions and cancers, and contribute to a broader clinical picture where cell damage is suspected.
