Clinical Utility of Lactate Dehydrogenase

Lactate dehydrogenase (LD), an enzyme in the glyco-lytic pathway (EC1.1.1.27; L-lactate: nicotinamide adenine dinucleotide [NAD +] oxidoreductase), catalyzes the oxidation of L-lactate to pyruvate with the mediation of NAD + as the hydrogen acceptor, with the reaction being reversible.1,2 This reaction forms the basis of the measurement of LD activity in the clinical laboratory with the rate of NADH production determined spectrophotometrically at 340 nm.3 LD has a molecular mass of 134 kDa; is a tetramer of two subunits, H and M; and hence has five isoenzymes, LD1 to LD5. While LD1 comprises four H subunits (H4), LD5 comprises only M subunits (M4), and the other isoenzymes LD2 to LD4 comprise H3M, H2M2, and HM3, respectively. It is a ubiquitous enzyme present in the cytoplasm of all cells, but the isoenzyme composition varies in various tissues. LD1 is predominant in heart, erythrocytes, and the kidney, while LD5 is predominant in liver and skeletal muscle. The other isoenzymes derive mainly from leukocytes, lymph nodes, lung, and spleen.1,2 Previously, the greatest indication for LD isoenzymes in serum was for the late diagnosis of myocardial infarction, in which one observed a “flipped pattern” …