Increased pre-operative platelet counts are a possible predictor for reduced sensitivity to heparin

We investigated a possible relationship between pre-operative platelet coun t and reduced sensitivity to heparin in 87 patients undergoing cardiac surg ery with cardiopulmonary bypass (CPB). Sensitivity to heparin was determine d by measuring the slope of the heparin dose response (HDR) before surgery. Pre-operative platelet counts were measured as pan of routine analysis of the patients' coagulation status. Patients with an HDR slope of <80 s u. ml (-1) were considered to have a reduced sensitivity to heparin and activated clotting time data were collected from these patients before and after hep arin administration before CPB. A significant correlation was determined be tween pre-operative platelet levels and HDR slope (P<0.001). Platelet count s were significantly greater in heparin-resistant patients compared with th ose who had the expected response to the anticoagulant (P<0.05). This could be caused by an increased capacity to produce platelet factor 4, which neu tralizes heparin.