ABO blood groups as risk factors for thrombosis

To evaluate the relationship between ABO blood group and thrombosis, we studied 127 patients taking oral anti-vitamin K drugs for thromboembolism prophylaxis and compared them with 700 voluntary blood donors. There were 68 patients with venous thrombosis (VT)-68 with deep vein thrombosis and 8 with pulmonary embolism-and 51 patients with arterial embolism (AE). There were 61 men and 66 women. Mean age at diagnosis was lower for all women, regardless of if they had VT or AE (43 years) than for men (55 years; Kruskal-Wallis test, p < 0.01). There was an imbalance between blood group A and O frequencies in patients with VT versus blood donors, with a higher frequency of blood group A or a lower frequency of blood group O, represented by a high A/O ratio. A/O ratio for blood donors was 0.63; it was 1.50 for men (Fisher test, p = 0.028) and 1.44 for women (Fisher test, p = 0.010). Patients with AE showed the same discrepancy, but it was significant for women (A/O = 2.25; Fisher test, p = 0.026) and not for men (A/O = 0.86; Fisher test, p = 0.836), suggesting that men with AE might have other risk factors for thrombosis. These data are not conclusive about the causes of the association between ABO blood groups and thrombosis, and prospective studies are needed to verify whether blood typing could have a predictive value for prophylatic measures in clinical and surgical patients.