Bacterial and viral contamination of donated blood remains a central safety concern in transfusion medicine despite substantial advances in screening and processing. We conducted a systematic review of laboratory based studies that directly tested donor blood or blood components for bacterial contamination (culture, rapid tests, or flow cytometry) or for transfusion-transmitted viruses using nucleic acid testing (NAT). We searched major databases from inception through October 28, 2025, selected original laboratory studies, and synthesized outcomes narratively due to methodological heterogeneity. Twelve original studies were included: six evaluated bacterial contamination (including large multicenter platelet culture programs and hospital blood-bank surveillance from Africa), and six evaluated NAT yields for HIV, HBV, and HCV among blood donors in Asia. Across high-income platelet programs, confirmed bacterial contamination was rare but non-zero, whereas several low- and middle-income settings reported higher contamination of stored whole blood. NAT programs consistently identified additional window-period infections that serology missed, with HBV typically contributing the highest yield. Overall, the evidence supports layered risk mitigation, primary culture with large-volume delayed sampling (LVDS) or validated rapid methods for platelets, strict aseptic practice for whole blood, and routine NAT where feasible. Standardized reporting and broader implementation of modern methods would further reduce transfusion-transmitted infections globally.