Leukocyte counts in 7,739 healthy black persons: effects of age and sex.

White blood cell counts (WBC) were measured in 7,739 healthy black individuals, ages one through 84 years, to determine normal values for different age and sex groups. The mean WBC was highest in children one to two years of age, regardless of sex. The mean count decreased progressively in both males and females during preschool years, reaching a nadir in females six to 10 years of age and in males 11 to 15 years of age. Females in the age groups 11 to 15, 16 to 20, 21 to 30, and 31 to 40 years had consistently higher mean WBC than males in the same groups (p less than 0.001, p less than 0.001, p less than 0.001, and p = 0.01, respectively). These differences may be ultimately related to hormonal physiology during the reproductive years, since they were not present in the older age categories (41 to 50, 51 to 60, and over 60 years). In both males and females over 60 years of age, the mean WBC was lower than in the 21 to 50 years age group. The mean and percentile values for each age and sex group from this large, healthy, non-institutionalized population can be used as a reference for normal WBC in black subjects.