Influence of climate on donor deferrals.

The purpose of this study was to ascertain the cause for seasonal variations of donor deferral. Deferred donors and monthly temperatures from 1981 to 1984 were tallied and analyzed. Temperatures were categorized at 10-degree intervals from 15 degrees F to 75 degrees F. Donors failing the hemoglobin screening then underwent a microhematocrit evaluation. Of the 65,531 donors seen at this blood center, 4537 were deferred, for an annual deferral rate of 6.7 to 7.2 percent (p less than 0.1). Deferrals for low hematocrit were significantly higher for both sexes at and above 45 degrees F. Similar experiences were also observed in 79,563 donors who came to the bloodmobiles over 19 months in 1983 and 1984. The percentages of deferrals at the blood center for low hematocrit in 1984 were 1.22, 2.6, and 3.5 for men and 6.7, 11.3, and 13.2 for the women at monthly average temperatures of 15.1 to 45 degrees F, 45.1 to 65 degrees F, and 65.1 to 75 degrees F, respectively. These differences of deferral rates are significant (p less than 0.05-0.001). Although other personal demographics remained constant, more of the donors deferred in this study had also been deferred in the past. The climatic changes had a significant effect on the blood composition that resulted in the deferral of blood donors with a borderline low hematocrit.