Exposure to sub-zero temperatures down to -11 °C does not impact packed red cells storage quality

European guidelines require packed red blood cells (pRBC) to be stored at 2-6 °C. However, negative temperature shifts can occur especially in prehospital transfusion. We investigated the impact of sub-zero temperature exposure on pRBC storage quality. At day 6 post donation (D6), three cohorts (14 pRBC) were put on a supercooled table for 10 h at either - 1 °C, -5 °C, and - 11 °C and compared to a control cohort. Hemolysis, pH and plasma biochemistry were evaluated weekly until D49. Storage-induced micro-erythrocytes (SMEs) were quantified as a surrogate marker for transfusion recovery. The primary endpoint was compliance with European storage standards at D42. The three sub-zero-exposed cohorts met standards at D42. Differences in hemolysis, pH, plasma biochemistry, or SMEs between exposed and control cohorts were non-statistically and/or non-clinically significant. Ten hours exposure to sub-zero temperatures down to -11 °C by conduction maintains storage quality of pRBCs, enabling a wiser risk assessment for potential transfusion use.