RESUMEN
BACKGROUND: Low hemoglobin (Hb) is the most common reason for temporary blood donor deferral. However, factors that affect Hb measurement may not portray donor health but reflect external circumstances. STUDY DESIGN AND METHODS: The effects of season, time of day, donor age, ABO, and D on capillary blood Hb level (cHb) and low Hb deferral were analyzed in 1,396,645 donor registrations from the years 2010 to 2014 in a national blood bank. RESULTS: cHb was lower in the summer (July mean 154.1 g/L in men, 139.6 g/L in women) and in the evening (7 pm mean 153.8 g/L in men, 138.9 g/L in women) than in the winter (January mean 156.9 g/L in men, 141.8 g/L in women) and in the morning (11 am mean 157.2 g/L in men, 142.8 g/L in women; all p < 0.0001). This affected donor deferral due to low Hb, with 7.8% donors deferred in July at 7 pm and 1.6% deferred in January at 11 am (p < 0.0001). With age, cHb increased in women and decreased in men. The lowest cHb was observed in blood group A (mean 154.9 g/L in men, 140.3 g/L in women) and the highest in blood group B (mean 156.6 g/L in men, 141.5 g/L in women). D had no practically significant effect on cHb. CONCLUSION: External factors, which do not reflect donor health, affect cHb and donor deferral due to low Hb. These factors should be considered when donor eligibility guidelines and procedures are developed.