Smoking, oral contraceptives, and obesity. Effects on white blood cell count.

Data from 14,961 healthy women were analyzed to determine the relative importance of factors that alter the white blood cell (WBC) count. The effects of smoking, oral contraceptive use, and obesity were most striking. A total leukocyte count greater than 10,00/cu mm was found in 44% of obese, heavily smoking women who took oral contraceptives (central 95% of the distribution was 5,800 to 14,200/cu mm) as compared to 2% of women without these attributes (3,500 to 9,400/cu mm). Other factors such as age, time of day, phase of the menstrual cycle, and red blood cell variables were of lesser significance. The use of noncontraceptive estrogenic hormones did not affect the WBC count. Recognition of these findings is important because excessive laboratory studies, lost physician time, and patient inconvenience may thereby be avoided.