Relationship between number of platelet transfusions and platelet increments at 1 hour and 18 to 24 hours after transfusion and days to next transfusion. (A) The mean 1-hour posttransfusion platelet increments are plotted for the first 25 transfusions given to all study patients. These data represent 6334 transfusions given to 533 patients (•). Similar data for the 18- to 24-hour posttransfusion platelet increments are shown for 5555 transfusions given to 531 patients (○). Data for days to next transfusion for 5955 transfusions given to 530 patients (▴). (B) When the same analyses are plotted for only lymphocytotoxic antibody-negative patients, the results are similar. One-hour increments for 5484 transfusions given to 477 patients (•), 18- to 24-hour increments for 4833 transfusions given to 475 patients (○), and days to next transfusion for 5144 transfusions given to 474 patients (▴). Dotted lines are best fit of the data for 1-hour posttranscription increments; dashed lines, for 24-hour posttransfusion increments; and solid lines, for days to next transfusion.