Anticoagulant effects of nonionic versus ionic contrast media in angiography syringes

To determine whether nonionic contrast media present a clotting hazard when plastic or glass injection syringes are contaminated with aspirated blood, we evaluated two nonionic (iohexol and iopamidol) and two ionic (ioxaglate and diatrizoate) contrast agents. We used a blood:contrast media ratio of 2 mL:5 mL and ten normal donors, each studied at 10, 20, 30, and 60 minutes, a parallel study of clotting and fibrinopeptide A (FPA) generation in plastic tubes, and life table analysis to estimate more accurately donor-based early clotting probabilities. While ionic contrast media are stronger anticoagulants, both nonionic and ionic media retard clotting in plastic tubes, and clotting in plastic and glass angiography syringes in comparison to saline controls. A clotting probability of 1% for nonionic agents in plastic syringes was not reached until a time (mean +/- SD) of 21.5 +/- 3.2 minutes. This contrasts with a time of 8.7 +/- 2.5 minutes for saline control. With plastic syringes, no clotting at all was observed at 10 and 20 minutes with either class of agents. Neither class of agents hastened the generation of FPA. We found no evidence, therefore, that nonionic agents either cause clots or are procoagulant.