Sentinel trends in donor hemoglobin values and low‐hemoglobin deferrals in a large US blood center

BACKGROUND: Low hemoglobin (Hb) is the leading cause of blood donor deferral yet mean Hb values are seldom examined as sentinel indicators of changes in donor recruitment, assessment, or testing. Case in point, following unexplained improvement in these parameters, U.S. blood centers observed a sharp rise in low-Hb deferrals after the 2024 introduction of a new international calibrator for some fingerstick hemoglobinometers. METHODS: We retrospectively analyzed 15 years (2010-2024) of allogeneic donor data from a national blood center. Mean donor Hb and low-Hb deferral rates were trended overall and by sex, cognizant of temporal practices affecting values like a ferritin testing program, the 2016 male Hb cutoff adjustment, and acceptance of allogeneic donors with testosterone-associated polycythemia. RESULTS: Among >11 million presentations (49.8% female), mean Hb values rose progressively from 2016 through 2023, correlating with a suspected gradual positive bias from a degrading hemoglobinometry standard. Female low-Hb deferrals declined from 12.2% (2016) to 7.7% (2023) before rebounding to 2016 levels in 2024 following recalibration. Male mean Hb trends were additionally influenced by increasing testosterone use in the donor base and the higher 13.0 g/dL Hb cutoff. Ferritin-based deferral programs temporarily raised mean Hb and reduced low-Hb deferrals, which reversed when suspended. DISCUSSION: Hemoglobinometer calibration drift, a ferritin testing policy, and donor testosterone use together shaped long-term donor Hb trends. Surveillance of mean donor Hb should be treated as a sentinel metric, and unexpected declines and increases in related deferral rates warrant the same scrutiny to protect both donors and blood availability.