Occasionally patients show little/no increment in the platelet count after platelet transfusions. This is called platelet refractoriness. May be due to physical or immunological mechanisms in the patient. The commonest physical mechanism is of platelet circulatory half-life reduction caused by concurrent sepsis or coagulopathy e.g. DIC. Immunological causes include induction of anti-HLA antibodies due to allosensitisation from previous transfusions or generation of anti-platelet antibodies such as in ITP. Investigation should be considered if platelet transfusions fail to maintain a platelet count >10 x 109/L at all times.