Race, ABO blood group, and venous thromboembolism risk: not black and white.

BACKGROUND The rate of venous thromboembolism (VTE) has been reported to be higher in blacks compared to whites. Non-O blood groups have also been associated with a significantly higher VTE risk. Given that a higher proportion of blacks have O blood group, one might have expected that black individuals would have fewer VTEs. STUDY DESIGN AND METHODS In this study, we analyzed race, sex, age, ABO or Rh blood group, and VTE risk in 60,982 black and white patients admitted over a span of 10 years. RESULTS The overall occurrence of VTEs was 7.6%, higher in males (8.7% males vs. 7.2% females), higher in non-O blood groups (8.5% non-O vs. 6.9% O blood group), and increased with age (5.8% <65 years, 11.3% ≥65 years). No difference in VTE rate was noted with Rh antigen positivity. When stratified by age, VTE rate was consistently higher in blacks and non-O blood groups. No difference was detected among the various non-O blood groups. To assess the potential confounder of comorbidities, we stratified patients according to Charlson comorbidity score. In a subgroup of healthy patients with age-independent Charlson comorbidity scores of 0 (n = 28,387), blacks still had an increased VTE risk and this risk was still higher with increasing age and in those with non-O blood groups. CONCLUSION We conclude that black race and non-O blood groups have increased VTE risk when stratified for age and that associated comorbidities do not explain these differences.