Interactions of platelets with standard heparin and low molecular weight fractions.

The availability of fibrinogen receptors on platelets after ADP stimulation, was investigated in order to analyze platelet hyperaggregability induced by heparin. Unfractionated heparin increased the binding of fibrinogen on ADP-treated platelets. The results varied according to both the donor platelets and the kind of heparin preparation used. Beef lung heparin was more active than porcine intestinal mucosa heparin (P less than 0.001). Low molecular weight (LMW) heparin fractions however did not significantly increase the binding of fibrinogen to ADP-treated platelets. The effect of standard heparin and LMW heparin on the aggregation of normal platelets induced by the addition of plasma from patients with heparin-induced immune thrombocytopenia was also studied. Concerning heparin-induced immune thrombocytopenia we have shown that the plasma cofactor present in some patient plasma may induce platelet aggregation both in the presence of standard-heparin and in the presence of LMW heparin fractions. Therefore, one has to be careful when replacing standard heparin by LMW heparin or heparinoids since each patient may react differently.