BACKGROUND: Recently, bleeding has been used in platelet (PLT) trials rather than surrogate outcomes. The purpose of this study was to provide a descriptive summary of data from PLT studies conducted in four countries and exploratory analyses to determine the relationship between bleeding and PLT count. STUDY DESIGN AND METHODS: A descriptive analysis was performed on original data from the Italian trigger study, the US TRAP study, the Canadian febrile reaction study, and a clinical chart review from one hospital site in the United Kingdom. The relationship between bleeding and PLT count was explored with the Italian data. RESULTS: A total of 897 patients with acute leukemia received 10,506 PLT transfusions. Grade 3 or Grade 4 WHO bleeding frequency was 28.1 percent (252/897) but varied by country: Italy, 10.8 percent (27/250); United States, 36.4 percent (217/598); Canada, 18.9 percent (7/37); and the United Kingdom, 8.3 percent (1/12). Grade 1 or Grade 2 bleeding was reported only in the Italian study (46.4%[116/250] and 11.6%[29/250], respectively). The relative rates of WHO Grade 2, 3, or 4 bleeding for PLT counts in the ranges of 0 to 4, 5 to 9, 10 to 14, and 15 to 19 (×109/L) were 8.8, 1.9, 1.8, and 1.2, respectively, compared to those counts within the range of 20 to 29 (×109/L). CONCLUSION: The study provides descriptive data on PLT use and frequency of bleeding. When PLT counts were 0 × 10 9 to 4 × 109 per L there was an eightfold increase in bleeding and a twofold risk increase when counts were 5 × 10 9 to 14 × 109 per L compared to the 20 × 109 to 29 × 109 per L reference range. The increased rate of bleeding at low counts occurred despite PLT therapy.
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