of platelets may be needed. The number of transfusions may be reduced if these patients are given recombinant human factor VIIa since the underlying cause are antibodies to platelet glycoproteins IIb/IIIa. Cardiopulmonary bypass surgery Cardiopulmonary bypass surgery can result in destruction of a large proportion of the patient's platelets and may render the remaining viable platelets dysfunctional. The indications for transfusion in such patients is controversial. General guidelines recommend not transfusing patients prophylactically but only when they are bleeding excessively, while also giving desmopressin. Drug-induced platelet dysfunction The most common of these is aspirin, and its similar drug class, the NSAIDs. Other antiplatelet drugs are commonly prescribed for patients with acute coronary syndromes such as clopidogrel and ticlopidine. When surgery is undertaken following the administration of these drugs, bleeding can be serious. Transfusion under these circumstances is not clear-cut and one has to use clinical judgment. Expected platelet increase after transfusion Platelet count increase as well as platelet survival after transfusion is related to the dose of platelets infused and to the patient's body surface area (BSA). Usually these values are less than what would be expected. Corrected platelet count increment (CCI) = platelet increment at one hr x BSA (m2) / # platelets infused x 1011 Expected platelet increase (per μL) = platelets infused x CCI / BSA (m2) The theoretical value of the CCI is 20,000/μL but clinically, the value is closer to 10,000/μL. If the CCI is less than 5,000/μL, patients are said to have "refractoriness" to platelet transfusion. Platelet collection The separation of individual blood components is done with a specialized centrifuge (see apheresis). The earliest manual forms of thrombapheresis are done by the separation of platelets from multiple bags of whole blood collected from donors or blood sellers. Since each blood bag (usually 250 mL or 500 mL) contains a relatively small number of platelets, it can take as many as a dozen blood bags (usually from five to ten bags, depending on the size of the blood bags and each donor's platelet count) to accumulate a single unit of platelets (enough for one patient). This greatly increases the risks of the transfusion. Each unit of platelets separated from donated whole blood is called a "platelet concentrate". Modern automatic thrombapheresis allows blood donors to give a portion of their platelets, while keeping their red blood cells and at least a portion of blood plasma. Therefore,