Frequency and distribution of ABO and Rh blood group systems among blood donors at the Northern Zone Blood Transfusion Center in Kilimanjaro, Tanzania: a retrospective cross-sectional study.

Majority of the donors had blood group O and also the vast majority of the donors were Rh positive. Considering the large size of our study population, this has provided a more comprehensive information regarding the frequency and patterns of ABO and Rh blood group systems in Tanzania. The observed association of blood group A with one of the regions from which donors were coming from, is intriguing and further studies may confirm possible related genetic evolution.