Effect of heparin on in vitro platelet reactivity in cardiac surgical patients--a comparative assessment by whole blood platelet aggregometry and haemostatometry

The in vitro effect of heparin on platelet reactivity was assessed simultaneously by haemostatometry (response to shear stress) and whole blood platelet aggregometry response to collagen (WBPA). From each blood sample a ratio (HR for haemostatometry and MR and IR for WBPA) showing platelet reactivity in the presence or absence of heparin (5 U/ml) was calculated. A value less than 1 represented a proaggregatory effect and greater than 1 an inhibitory effect. Non-anticoagulated blood samples obtained from 290 cardiac surgical patients were tested by haemostatometry and citrated whole blood samples from 100 patients with aggregometry. Haemostatometry demonstrated a proaggregatory effect of heparin in 8.6% (25) and an inhibitory effect in 91.4% (265). Assessed by WBPA, heparin was proaggregatory in 41-46% and inhibitory in 54-59%. In the 100 patients tested by both methods there was a significant correlation between the findings with the two techniques (r = 0.46, p less than 0.0001). A wide individual variation in the platelet effect of heparin was demonstrated. This variation appeared greater and a higher proportion showed inhibition when blood was tested by haemostatometry.