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The determinants of frequent donation and factors that lead to high return rates among volunteer blood donors are increasingly important as the eligible donor population continues to be reduced. Deferrals for medications, travel, lifestyle, and emergent diseases and the increasing age of the donor population decrease the pool of available donors. To address concerns about the adequacy of the blood supply, blood centers need to not only recruit new donors but to understand what motivates donors to give again to improve donor retention and increase donation frequency. Previous studies have suggested that the total number of first-time donors is decreasing1 and that only 8% of those new donors continue donating.2 Other reports suggest that younger and minority donors were less likely to donate again within 12 months,3 shorter intervals between a first and second donation increased the likelihood of subsequent donations,4 and first-year donation frequency is a strong predictor of long-term donor return.2 Variables such as age, ethnicity, blood type, and education have also been shown to influence donor return behavior.4 The Retrovirus Epidemiology Donor Study-II (REDS-II) Donor Iron Status Evaluation (RISE) study was a prospective cohort study of hemoglobin (Hb) and iron metabolism in first-time and frequent blood donors. By the midpoint of the 15-month study it became clear that RISE subjects in both cohorts were presenting to donate blood more frequently than predicted. This analysis sought to determine if the reason(s) for higher-than-expected donor return rates involved the donor’s participation in a nonremunerated study.

Blood centers are interested in understanding determinants of frequent blood donation. We hypothesized that participation in uncompensated research could result in higher donation rates.Donation rates for 2425 subjects from six US blood centers enrolled in the Retrovirus Epidemiology Donor Study-II Donor Iron Status Evaluation Study were compared to those of nonenrolled donors (n = 202,383). Over 15 months, we compared mean donation rates and adjusted rate ratios (RRs) between enrolled and nonenrolled for three subgroups, first-time, reactivated, and frequent donors, and donation rates before and after the study enrollment period for frequent donors only.Enrolled donors had higher 15-month mean donation rates than nonenrolled donors (first-time, 1.21 [RR = 1.91]; reactivated, 1.68 [RR = 1.83]; frequent, 3.40 [RR = 1.12]). However, frequent donors donated at approximately the same rate after enrollment as they did before enrollment in the study (3.62 per 15 months [RR = 1.12]).Donors enrolled in the study donated at a higher rate than nonenrolled donors, but frequent donors remained consistent in their donation frequency both before and after enrollment. Although increased donation rates could have been causally related to study enrollment, we cannot rule out an enrollment bias whereby more committed donors were more likely to enroll in the study.