[The phenomenon of relative resistance to heparin]

In a prospective clinical study heparin half-life and in vitro and ex vivo heparin sensitivity, as assessed by activated partial thromboplastin time prolongation, was evaluated in 8 healthy volunteers and in 21 patients with malignant tumor. In the patients, coagulation activation was evaluated by determining the fibrinogen half-life and the level of the fibrin-fibrinogen degradation products. The results were comparable in the two groups of subjects, and in the patients there was no correlation with the degree of activation of the coagulation system. In both groups large interindividual variations were recorded. These results confirm those obtained in patients with deep venous thrombosis. They suggest that the relative heparin resistance phenomenon encountered in some patients during heparin therapy is unrelated to the presence of the thromboembolic disease (P.M.).