Time to refractoriness of the initial donor's platelets. Time to refractoriness expressed as a percentage of the recipients who continued to accept STD or treated platelets from their initial donors is shown. The recipient dogs are categorized by the type of platelets they received (ie, both filter and centrifuge leukoreduced [F-LR/C-LR], γ-irradiation with F-LR/C-LR [γ-F-LR/C-LR], filter leukoreduced using 1 or 2 filters [F-LR], centrifuge leukoreduced [C-LR], or standard [STD] platelets). The transfusion week is given on the abscissa and the percentage of accepting recipients remaining in each group on the ordinate. P values for the comparison of each group to the STD group were F-LR/C-LR, P = .001; γ-F-LR/C-LR, P = .004; FL, P = .86; and C-LR, P = .21. Because of multiple comparisons, a P value of .01 or less was considered significant.