Effect of heparin in nonionic contrast media on blood coagulation and its dose response curve

To investigate the local effect of heparin on blood clot formation and partial thromboplastin time (PTT), blood was withdrawn into the catheters filled with iopamidol and heparin at 0, 1, 2, 3, 5, and 10 U per ml concentrations as debubbling. After 30 min incubation, blood clotting was observed in all 8 experiments with heparin concentrations of 0 and 1 U per ml; in 3 of 8 with 2 U per ml; and in none with ≥ 3 U per ml. PTT of blood and contrast mixture in catheters increased significantly when heparin concentrations were increased from 2 to 3 U per ml and reached a level of > 110 sec at 5 or more U per ml. Thus, the addition of heparin to nonionic contrast media at concentrations of 5 U per ml may be an easy measure with which to prevent blood clotting and reduce thromboembolic complications during coronary arteriography.