Platelet demand is unpredictable and will relate to case mix, programmes of treatment requiring intensive platelet support and health service activity. Other relevant factors include the impact of clinical practice guidelines which have the potential when implemented to reduce the increase in demand or supress the clinical application of platelet component transfusion (Morris, K. 2018). Although platelet transfusions are vital to the ongoing management of patients with haematological malignancies, many patients become refractory to platelet transfusion. Refractoriness is defined as having a poor response (immediate or 24-hour increment post platelet transfusion of <10 x 109/L) to random donor platelets on two or more occasions. Refractoriness can be due to either immune or non-immune mechanisms. Most platelet refractory cases are thought to be non-immune with the minority due to anti-platelet antibodies and thus immune. This project was performed to see if platelet increments could be improved by providing crossmatch compatible platelets for haematology patients with non-immune platelet refractoriness in addition, to provide more information on the possible effect of complement on platelet activation and destruction. P-selectin and complement markers C1q, C3 and C3dg were compared in patient’s pre and post transfusion and in apheresis and whole blood derived platelet donations to identify any association with poor platelet increments. The results showed that the provision of crossmatch compatible platelets did not improve platelet increments. Comparison of the two platelet manufacture methods showed that apheresis platelets had higher levels of P-selectin and complement components C1q and C3 on them. However, this did not account for the poor increments or incompatible crossmatches