Classic Coagulation Traits Vary According to Rh(D) (But Not ABO) Blood Groups

<b>Background:</b> This study evaluated possible variations in classic blood coagulation parameters according to groups formed from the main erythrocyte antigen systems. <b>Methods:</b> Consecutive patients admitted to a transfusion hemotherapy service at a private hospital in the Brazilian Federal District were evaluated for coagulation profile and blood type according to routine laboratory practices. The international normalized ratio (INR), the activated partial thromboplastin time (APTT) and the prothrombin time (PT) were compared according to the ABO blood group and the Rh factor in analyses controlled for classic influencers such as age, sex and comorbidities. <b>Results:</b> No significant differences in coagulation were found between groups defined by the ABO antigen system, despite a body of evidence in favor of this correlation. Rh-positive individuals showed increased mean values in PT (13.7 vs. 12.6 s), in APTT (32.0 vs. 30.1 s) and in INR (1.23 vs. 1.15 s) when compared to the Rh-negative counterparts. <b>Conclusions:</b> Our results suggest a lowered rate of coagulation among Rh-positive individuals, possibly owing to inhibitory effects of the Rh(D) erythrocyte antigen on the coagulation pathway.