LDH is widely distributed in tissue, particularly, liver, muscle, and kidney. LDH in serum can be separated into five different isoenzymes based on their electrophoretic mobility. Each isoenzyme is a tetramer composed of two different subunits. These two subunits have been designated heart and muscle, based on their polypeptide chains. There are two homotetramers, LDH-1 (heart) and LDH-5 (muscle), and three hybrid isoenzymes. Elevated serum levels of LDH have been observed in a variety of disease states.
The highest levels are seen in patients with megaloblastic anemia, myocardial infarction, disseminated carcinoma, leukemia, and trauma. Mild increases in LDH activity have been reported in cases of hemolytic anemia, muscular dystrophy, pulmonary infarction, hepatitis, nephortic syndrome, and cirrhosis.
The lower frequency of replicated errors in LDH measurement observed using serum samples centrifuged according to manufacturer’s instruction suggests that assay precision in serum is better if samples are centrifuged at 1300 g rather than 2000 g when the International Federation of Clinical Chemistry-recommended procedure is used.
Hemolysis due to the breakdown of red blood cells is important to the laboratory because it will cause increased test results for specific tests like potassium and lactate dehydrogenase
