Alterations of Erythrocyte Lactate Dehydrogenase in Man

Erythrocyte preparations from normal men and women contain 5 isoenzymes of lactate dehydrogenase in constant proportions. LDH-5 is found exclusively in younger cells, and LDH-1 is the predominant fraction of aged erythrocytes. The apparent increase of LDH-1 in aged cells represents loss of activity of isoenzymes containing labile M subunits and not synthesis of H subunits.

When erythrocyte isoenzymes from patients with hematologic disease are assayed, increases in LDH-5 indicate active or hyperactive erythroid tissue, and absence of this fraction suggests nonfunctioning tissue. An increase in the relative percentage of LDH-1 suggests the presence of an older cell population. Thus the analysis of erythrocyte LDH isoenzymes appears to have clinical value in rapidly assessing erythropoietic activity.