The relationship between thrombus weight and aPTT ratio (A) and plasma aPC concentration (B) in the guinea pig thrombosis model. PC variants were infused for 15 minutes before and throughout a 15-minute period of blood circulation through the shunt. Thrombus weight, blood aPTT, and plasma aPC concentration were determined at the end of the 30-minute infusion. Plasma concentration of aPC was determined using an immunocapture amidolytic assay.