Red blood cell aggregation versus blood clot formation in ionic and nonionic contrast media

The effects of ionic and nonionic radiographic contrast media on human blood in plastic syringes were investigated in an in vitro double-blind study. Venous blood, which was drawn into plastic syringes containing one of four (iohexol, iopamidol, diatrizoate sodium meglumine, and ioxaglate sodium meglumine) contrast media, was visually inspected at predetermined time intervals before and after mixing. Aliquots of the mixtures of blood and contrast media also were evaluated microscopically. Irregular red blood cell (RBC) aggregates were observed with the nonionic contrast media. Pronounced RBC morphologic alterations occurred with diatrizoate (ionic), and marked crenation was observed with ioxaglate (ionic). Observed aggregates were freely disaggregated in isotonic saline. Recovered supernatant blood from centrifuged aliquots of the mixtures was evaluated for clot formation. There was no evidence of blood clot formation within 1 hour after blood was introduced into syringes containing either ionic or nonionic contrast media. This time period exceeded the normal clotting time, since blood in syringes without contrast media formed clots within 30 to 45 minutes. Both the nonionic and ionic contrast media prolonged coagulation.