Liver Function Tests
Liver Function Tests
 

Lactate Dehydrogenase

 
 
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Overview

  • 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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