Demographic Risk Factors for Low Hematocrit (HCT) Deferral in Regular Whole Blood Donors.
Authors: Mast Alan E. , Schlumpf Karen S. , Custer Brian ,   NHLBI Retrovirus Epidemiology Donor Study-II4
Published: October 2019

Abstract
Introduction: The most common cause of deferral of whole blood donors is HCT below 38%. 15% of previously successful donors deferred for low HCT do not return within a 5-year period (Transfusion2007, 47:1514). Identification of the causes for low HCT deferral is important to define new donor management strategies and maintain an adequate blood supply. We sought to define risk factors for low HCT deferral among previously successful whole blood donors.
Methods: The REDSII database tracked >750,000 whole blood donors at the 6 REDSII blood centers between January 2006 and March 2007. Donors were stratified by whole blood donation intensity and then by gender, age, race and education level. The rate of low HCT deferral was determined by dividing the number of donors with HCT deferral by the total number of donors in each donation intensity and demographic stratum. Plots of donation intensity (x-axis) vs. HCT deferral rate (y-axis) were used to generate low HCT deferral curves. For the donation frequency (1 to 5) during this time period the slopes of the deferral curve are linear (r2>0.98) and provide a measure for comparison of the sensitivity/resistance of each group to low HCT deferral.
Results: Women less than 51 years old have the steepest deferral slope (0.068-meaning a 6.8% increase in low HCT deferral with each increase in donation frequency). The slope is identical in women of all race/ethnicity and education groups suggesting that menstrual status is the single most important predictor of low HCT deferral in frequent female donors. The deferral slope decreases in post-menopausal women between 51 and 70 years old (0.046) but never approaches that of men (0.011) suggesting that women do not readily replenish iron stores following cessation of menses. The deferral curve slope in men increases with each decade of life beginning at age 50. An increase is also observed in women >70 years old and demonstrates that donors >50 progressively become less able to respond to the stress of blood donation. Studies of race/ethnicity in male donors demonstrated somewhat unexpected, yet distinct, differences. Men of Asian descent have a much lower deferral slope (0.0035) than white (0.011) or Hispanic (0.012) donors, while African-American donors (0.021) have a much higher deferral slope. There are several possible explanations for these data including hemoglobinopathies or genetic set point for HCT. However, it is also plausible that there are genetically regulated differences in iron absorption in response to the stress of repeated whole blood donation. Studies of education level in males also demonstrated differences. The deferral curve is steepest for high school graduates (0.015) and decreases with increased education, some college (0.012), bachelor’s degree (0.0089), and master’s degree or higher (0.0082).
Conclusions: Rates of low HCT deferral in well-defined groups of whole blood donors were examined as a function of donation intensity. Gender, age, race and education based differences in the ability to repeatedly donate whole blood were identified. These data lay the ground work for devising personalized blood donation intervals that may reduce the incidence of low HCT deferral among previously successful donors. They also provide important, new epidemiological information that may help us better understand diverse issues such as the anemia of aging and genetically regulated controls of iron absorption.