Refractoriness to platelet transfusions and bleeding complications are the main clinical problems in intensively treated hemato-oncological patients and are essential endpoints for transfusion studies as well. In this trial, bleeding will be scored according to the World Health Organization (WHO) scale as a primary endpoint. Refractoriness is defined as a 1-hour CCI <7.5 and/or a 24-hour CCI <4.5 after ABO compatible platelet transfusions on at least two successive occasions. Known causes of non-alloimmune refractoriness are included in this trial because for the purpose of generalization, relevant to develop a national product, testing transfusion efficacy of new platelet products should imply all patients in need of a preventive support with platelet transfusions. The 1- and 24-hour CCI are commonly used to evaluate platelet transfusions and, albeit not without discussion, currently the platelet count is the only parameter in trigger-based transfusion policy. The ratio of both the 1-hour and 24-hour CCI mirrors both platelet recovery immediately after transfusion as the 1-hour CCI, and platelet survival one day after transfusion as the 24-hour CCI. Other secondary clinical endpoints of the trial will be transfusion requirement (red cells and platelets), transfusion interval to next transfusion and adverse reactions.