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

The 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 (H_R for haemostatometry and M_R and I for WBPA) showing platelet reactivity in the presence or absence of heparin (5 U/ml) was calculated. A value < 1 represented a proaggregatory effect and > 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 < 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.