The blood assignment problem is an important real-world optimization problem because of the continuous demand for blood transfusion during medical emergencies. The formulation of this problem stretches from managing critical blood shortage levels and blood unit expiration, to blood compatibility between donor and patients. Another contributing factor to the blood assignment problem lies in the blood bank having to import additional blood units from external sources when supply cannot meet the

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... mand. These challenges have serious consequences especially in the case where the demand for the blood is very high. Therefore, there is the need to minimize blood product wastage with regards to expiration and importation, whilst maximizing product delivery to patients in need. To solve this problem, existing studies used fixed percentage bounds to generate values for demand and supply of whole blood units. However, in this paper, a different approach is considered when generating such values, which involves allocating a unique percentage bound to each month. The bounds conform to statistics taken from South African social behavior with the attempt at generating values which mimic real-life monthly demand and supply of whole blood units. Furthermore, this study implements a hybrid metaheuristic algorithm that combines symbiotic organisms search algorithm with the blood assignment policy in relation to the blood banks of South Africa to effectively minimize the operational costs of the blood transfusion centers. The computational results indicate that the proposed algorithm performed quite satisfactorily from the computational time, stock-piling, and low importation level points of view. INDEX TERMS Blood assignment problem, blood product, blood group, blood compatibility, symbiotic organisms search algorithm, SOS.