Seasonal influences on hemoglobin levels and deferral rates in whole-blood and plasma donors

BACKGROUND: Indications exist that deferral rates in blood donors are highest in summer. However, a detailed quantitative analysis is not available. The association between Hb values, deferral rates, and daily temperatures was investigated in a large data set of blood donors. STUDY DESIGN AND METHODS: The study population consisted of both plasma and whole-blood donors from the southeast region of the Netherlands. Individual Hb levels and other examination data between January 2002 and December 2004 were extracted from the donor file. Data on daily maximum temperatures were related to Hb levels and Hb deferrals. Results are reported separately for plasma and whole-blood donors as well as for men and women. RESULTS: Data were available from 106,398 whole blood donors and 6983 plasma donors, resulting in data of more than 600,000 examinations. Hb levels decreased with increasing daily temperature. Highest deferral rates were observed in summer months, which were consistent over the several groups and over the three years. The highest Hb deferral of 11.1 percent was observed for female whole-blood donors on days with a maximum temperature of 25 degrees and above. In all four donor categories a gradual increase with temperature was observed with 1.7-2.2 times higher deferral rates on hot days (>= 25 degrees C) compared to cold days (< 5 degrees C). CONCLUSION: A clear seasonal pattern in Hb levels and in the percentage of Hb deferrals was observed. The observed seasonal effect could not be explained by differences in donor characteristics. Our observations might have practical implications for donor management.