LAUSR

Mehic et al. Association of ABO blood group with bleeding severity in patients with bleeding of unknown cause. Blood Adv. 2020; 4: 5157–5164. https://doi.org/10.1182/blood advan ces.20200 02452 Intensive laboratory investigation of patients presenting with mild/moderate bleeding tendencies fails to provide a definitive diagnosis in 30%-50% of cases. Nevertheless, these patients often have significant symptoms that interfere with their quality of life. Now, in a study of 422 patients with bleeding of unknown cause (BUC), Mehic and colleagues have reported an excess of blood group O in the bleeding disorder cohort compared to 23 145 healthy blood donors (47.2% vs 37.6%; odds ratio, 1.48; 95% CI, 1.22-1.79). The association of ABO blood group with plasma levels of VWF and FVIII are well recognized, but in this study the bleeding scores and numbers of bleeding symptoms were significantly higher in blood group O patients compared to non-O patients after adjustment for VWF and FVIII levels, and sex. Oral mucosal bleeding was more prevalent in blood group O patients vs non-O patients (26.1% vs 14.3%) also independent of VWF and FVIII levels, and sex. Patients with BUC showed evidence of increased clot density by two methodologies, but no differences in thrombin generation, clot lysis or platelet function. In conclusion, the role of ABO blood group (and by extension, differences in protein glycosylation status) in promoting normal hemostasis appears to be more pervasive than previously recognized, and deserves further study.