Correlation between ABO blood group and vaso-occlusive crisis among adult patients with sickle cell anaemia in northern Nigeria

Background In sickle cell disease (SCD), the vascular endothelium is in a continuous state of activation by inflammatory cytokines, leading to increased secretion of von Willebrand factor (vWF), which is a potent mediator of cytoadherence. Vaso-occlusive crisis (VOC) involves cytoadherence of sickle red cells, leucocytes and platelets onto vascular endothelium. Non-O blood groups are also associated with the elevation of vWF levels. Thus, SCD and non-O blood groups are independently associated with the elevated levels of vWF, which is an important cofactor in the pathogenesis of VOC. Objectives We hypothesized that SCD patients with non-O groups would have higher levels of vWF and greater risk of VOC than SCD patients with blood group O. If our hypothesis is correct, SCD patients with non-O groups would have higher frequency of VOC than those with blood group O. Materials and methods We conducted a retrospective study of frequencies of VOC with respect to ABO blood groups and vWF levels in 352 adult patients with SCD in Nigeria. Results In comparison with blood group O, patients with non-O blood groups had significantly higher mean levels of vWF (189 vs. 153%, P 0.05), significantly higher proportion of patients affected by VOC (75.8 vs. 34.2%, P 0.05) with a significantly higher mean number of VOC episodes per patient (3.2 vs. 1.5, P 0.05). The relative risk of VOC for patients with non-O blood groups was 1.94 (95% confidence interval 1.5-2.7, P = 0.004). Conclusion SCD patients with non-O blood groups had higher frequencies and risk of VOC that were attributed to the effect of higher levels of vWF. These data suggest that non-O blood group is a risk factor for frequent VOC and an adverse prognostic index in SCD. This preliminary report calls for further studies to precisely determine the clinical significance of ABO blood groups in SCD within the context of clinical subphenotyping.