Heparin effect on red blood cell aggregation.

We studied the effect of relatively high dosages of heparin (25-150 U/ml) on some rheological parameters of donor blood. It was found that heparin increased the erythrocyte sedimentation rate (ESR) and low shear blood viscosity at all concentrations studied. The increase of these parameters indicates an elevation in RBC aggregation. In all samples with a heparin concentration of 100 U/ml, the average ESR was increased by approximately 75% (p < 0.001); whole blood viscosity increased under shear rate, gamma = 0.277 sec-1, by approximately 30% (p < 0.001). Since bolus injection of heparin may result in transient high local concentration, these results suggest a possible additional adverse effect to the well known heparin effect on platelet aggregation.