Freshly isolated and stored platelets were plated on Cell-Tak coated plates and a modified mitochondrial stress test was performed with measurement of basal, followed by injection of oligomycin (1 µg/ml), HSA (150 µM), FCCP (0.6 µM for controls and 3.5 µM for HSA group) and antimycin A (10 µM). Representative bioenergetic traces of (A) freshly isolated and (C) stored platelets. Indices of bioenergetics including proton leak HSA (rate after HSA injection – rate after antimycin A injection) were calculated for (B) fresh and (D) stored platelets. Data expressed as mean±SEM, n = 3 individual donors for the freshly isolated and stored platelets. **p<0.01, different from freshly isolated.