Rapid platelet-function assay - An automated and quantitative cartridge-based method

Background-The platelet glycoprotein (GP) IIb/IIIa receptor is important in mediating platelet thrombus formation, and the GP IIb/IIIa antagonist abci ximab (c7E3 Fab; ReoPro) is effective in preventing thrombotic ischemic car diovascular complications of unstable angina and percutaneous coronary inte rventions. Small-molecule antagonists of GP IIb/IIIa based on the Arg-Gly-A sp (RGD) sequence show similar benefit, and some of these agents are orally active. However, there may be significant interindividual variation in res ponse to such antagonists, especially with chronic oral therapy. It will be essential to balance the beneficial antithrombotic effect of these drugs w ith their potential for causing bleeding. In response to this need, we have developed a rapid platelet-function assay (RPFA), a point-of-care system t hat provides a quantitative measure of the competence of the GP IIb/IIIa re ceptor as reflected in the ability of platelets to agglutinate fibrinogen-c oated beads. Methods and Results-Polystyrene beads were coated with fibrinogen and place d in a cartridge along with a lyophilized peptide that activates the thromb in receptor. Anticoagulated whole blood was added to the cartridge, and the n a microprocessor-controlled operation mixed the reagents and detected agg lutination between platelets and coated beads. Quantitative digital results were displayed within 3 minutes. Because there is no dilution of the blood , the assay can be used to measure platelet activity in samples that have b een treated with GP IIb/IIIa antagonists with high dissociation rates. RPFA results of whole-blood samples treated with different GP IIb/IIIa antagoni sts correlated well with both conventional turbidimetric platelet aggregati on (r(2)=0.95) and the percentage of free GP IIb/IIIa molecules in the samp le (r(2)=0.96). The mean difference in measurements between RPFA and aggreg ometry was -4% (+-4% SD), and the mean difference in measurements between R PFA and free GP IIb/IIIa receptors was -2% (+/-6% SD). Conclusions-The RPFA provides rapid information on platelet function that m irrors turbidimetric platelet aggregation and reflects GP IIb/IIIa receptor blockade.