ABO Group as a Thrombotic Risk Factor in Children With Acute Lymphoblastic Leukemia: A Retrospective Study of 523 Patients.

Children with acute lymphoblastic leukemia (ALL) are at high risk of thrombotic complications, resulting from multiple risk factors (malignancy, chemotherapy, central venous access devices, and inherent host characteristics). Non-O blood groups have been associated with an increased risk of venous thromboembolism (VTE) in adults, with a compounding effect in the presence of thrombophilia or cancer. We hypothesized that among children with ALL receiving a standardized protocol, there would be an increased risk of thrombotic events in non-O compared with O blood group patients. In a retrospective study of 523 children with ALL from June 1995 to April 2013, there were 56 (10.7%) thromboembolic events. Patients with VTE were compared with the whole cohort, based on blood group, age, sex, leukemia phenotype, and clinical risk category. Among children with VTE, 42 (75%) had non-O and 14 (25%) had O blood group, compared with 302 (57.7%) non-O and 221 (42.3%) O blood groups in the cohort. Non-O blood group was confirmed as an independent risk factor for VTE in multivariate analysis. This is the first study to report a significant association between non-O blood groups and VTE in children with cancer.