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Liver Function Tests

Lactate Dehydrogenase

February 15th, 2021
On this page:LDH Isoenzymes


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
  • Shock
  • Trauma
  • Hypoxia

LDH Isoenzymes

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.
  • Interpretation

  • 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
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