In 2013, nearly 15 million units of banked blood were transfused in the United States alone. Blood shortages are expected to increase globally. Donated blood is not equal due to differences in quality and deterioration rate. There are no methods to detect time-dependent biochemical and biophysical changes of RBCs or the deterioration rate of donated RBCs. Nine randomly selected RBC units collected by the San Diego Blood Bank were examined for inter-donor variability over six weeks of storage. In vitro RBC quality was assessed weekly by conventional biochemical tests including free Hb, K+, ATP, P50, 2,3 DPG, lactate, and pH. Deformability was measured via cell filtration. Briefly, the RBC suspension (10% Hct), was forced through a 5.0μm pore membrane (106 mm2) at various flow rates. No inter-donor variability in biochemical or mechanical parameters was observed at baseline. Inter-donor variability in biochemical properties (free Hb, K+, ATP, P50, 2,3 DPG, lactate, and pH) was observed after 14 days of storage. However, significant differences from baseline in RBC mechanical properties (i.e. filterability) were observed as early as 7 days into storage at the lowest flow rates and after 28 days of storage at all flow rates. There was a net decrease in filterability over time for all donors, but the rate at which filterability decreased (i.e. deterioration rates) was different when comparing individual donors. Changes in all biochemical parameters were significant different between donors. These data suggest that filterability is more sensitive to changes in blood quality than conventional biochemical parameters.