Hemoglobin A1c levels do not affect vasovagal risk in blood donors

Vasovagal reactions (VVRs) are the most common acute adverse events in blood donation. While younger age, lower body weight, and first-time status are known risk factors, the role of glycemic control in VVR risk is not well understood. Notably, some countries restrict donations from individuals with diabetes or those on anti-diabetic medications due to concerns about adverse reactions.

We analyzed data from 391,607 blood donors tested for hemoglobin A1C (HbA1C) in March 2025. Donors were categorized as normoglycemic (HbA1C <5.7%), or hyperglycemic (HbA1C ≥5.7%). The primary outcome was the occurrence of a VVR during or immediately after donation. Logistic regression stratified by sex was used to assess associations between HbA1C category and VVRs, adjusting for donor characteristics within each stratum of sex.

A total of 9394 VVRs were recorded in the study (2.4%). Varying glycemia levels were not associated with the risk of VVRs in female donors. Hyperglycemic male donors had lower odds of VVRs than their normoglycemic counterparts in adjusted models (odds ratio [OR] 0.72, 95% confidence interval [CI]: 0.62-0.83). Age, race/ethnicity, hemoglobin levels, and percent blood loss during donation remained strong independent predictors of VVRs in both sexes.

Higher-than-normal HbA1C levels were not associated with increased risk of VVRs regardless of sex. These findings suggest that glycemic status may not meaningfully impact donor safety and challenge policies that restrict donations based solely on glycemic control.