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

We investigated a possible relationship between pre-operative platelet count and reduced sensitivity to heparin in 87 patients undergoing cardiac surgery with cardiopulmonary bypass (CPB). Sensitivity to heparin was determined by measuring the slope of the heparin dose response (HDR) before surgery. Pre-operative platelet counts were measured as part 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 heparin administration before CPB. A significant correlation was determined between pre-operative platelet levels and HDR slope (P<0.001). Platelet counts were significantly greater in heparin-resistant patients compared with those 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 neutralizes heparin.