- Lactate dehydrogenase (LDH) is an enzyme present in the cytoplasm of most cells that catalyses the conversion of lactate to pyruvate.
- As LDH is present in all tissues, its elevation is a nonspecific marker of cell damage. Elevation of specific LDH isoenzymes may point toward a specific pathology, as below.
Causes of Elevated Lactate Dehydrogenase
- Factitious (haemolysed sample)
- Heart - myocardial infarction, heart failure
- Brain - ischaemic stroke, traumatic brain injury
- Kidneys - nephritis, nephrotic syndrome, acute tubular necrosis, infarction
- Anaemia - haemolytic or megaloblastic
- Malignancy (especially haematological)
- Lungs - pulmonary embolism, infarction, obstructive disease, interstitial lung disease, pneumonia
- Spleen - infarction
- Pancreas - pancreatitis
- Liver - hepatitis, infarction, cirrhosis, malignancy, trauma
- Skeletal muscle - strenuous exercise, rhabdomyolysis, myositis
- There are five LDH isoenzymes composed of two H (heart) and M (muscle) subunits. The isoenzymes are classified depending on their migration on electrophoresis.
- The isoenzyme electrophoresis pattern is relatively non-specific, though specific patterns of isoenzyme elevation are classically (yet loosely) associated with certain diseases.
- Elevated LDH1 and LDH2 - myocardial infarction, brain injury, renal pathology, haemolytic or megaloblastic anaemias
- LDH1 > LDH2 (‘flipped’ LDH) - myocardial infarction
- Elevated LDH2 and LDH3 - acute leukaemia
- Elevated LDH3 and LDH4 - splenic or lung pathology
- Elevated LDH5 - liver or skeletal muscular pathology