Cytochrome b5 reductase activity in erythrocytes and leukocytes as related to sex and age.

We measured cytochrome b5 reductase (EC 1.6.2.2) activity in erythrocytes and leukocytes from subjects of both sexes ranging in age from neonate to adulthood, all either apparently healthy or without hematologic disorders. The activities were determined spectrophotometrically (J. Lab. Clin. Med. 72: 339-344, 1968). Within-run precision (CV) of the reductase determination was 6.4% and 3.7% for erythrocytes and leukocytes, respectively. Activity in either erythrocytes or leukocytes was unrelated to sex. Activity was lowest in erythrocytes of newborns (p less than 0.001) but reached adult values within the first postnatal year. Leukocyte activity was higher (p less than 0.05) in infants one to 24 months old than in other groups, possibly because of variations in leukocyte count in the first postnatal months.