A 45-year-old man with chronic kidney disease (CKD stage 4) requiring a blood transfusion for symptomatic anemia (Hb 6.5 g/dL) is found to have a positive indirect Coombs test (IAT) on routine pre-transfusion screening. Direct Coombs test is negative. Blood bank reports the presence of an alloantibody (anti-Kell, anti-Duffy, or anti-Kidd) but cannot identify the exact specificity. What is the most appropriate next step in management?