Erythrocyte macrocytosis in feline leukemia virus associated anemia.

Using erythrocyte volume distribution histograms (erythrograms), erythrocyte macrocytosis and anisocytosis were quantitated in 139 cats tested for feline leukemia virus group-specific antigen. Feline leukemia virus-negative cats with non-regenerative anemia or normal packed cell volumes had normal mean corpuscular volume values. Uninfected cats with regenerative anemia had prominent significantly increased macrocytosis and anisocytosis (p less than 0.01). Ninety percent of 62 feline leukemia virus-positive cats had altered erythrograms. Thirty-three feline leukemia virus-positive cats with non-regenerative anemia had marked macrocytosis. Their mean corpuscular volume values (mean 60 fl +/- 2 fl standard error, reference range of 37-49 fl) were significantly greater than those of feline leukemia virus-negative cats except for those with regenerative anemia. Feline leukemia virus-positive, non-anemic cats had significantly increased mean corpuscular volume values of intermediate magnitude. Nine adult cats experimentally infected with feline leukemia virus developed non-regenerative anemia with significant increases in mean corpuscular volume and anisocytosis. However, the macrocytosis observed in these cats was considerably less than in naturally occurring feline leukemia virus-positive cats with non-regenerative anemia. These observations indicate there are events in the pathogenesis of feline leukemia virus-associated anemia other than simple erythroid hypoplasia. We suggest that hemolysis and erythrocyte regeneration occur before erythroid hypoplasia and may partially account for macrocytosis observed in the face of non-regenerative anemia.