Sialidase activity associated with fresh and stored platelets from 3 individual donors. Total sialidase activity in platelets was measured in nonpermeabilized RT platelets at day 0 and day 7 and in permeabilized RT platelets (n = 3). Total sialidase activity in platelets was measured in day-0 permeabilized RT platelets. The amount of 4-methylumbellyferone released in quenched reaction mixtures was measured in 96-well Microfluor-1 Black plates on a Spectra MAX GEMINI EM Microplate Spectrofluorometer (molecular devices) with excitation, emission, and cutoff wavelengths of 355, 460, and 455 nm, respectively. Background fluorescence was subtracted from each data point. Sialidase activity recorded at 3 hours is shown. The degree of significance is indicated as ∗P < .05, ∗∗P < .01.