Radiographic contrast agents and platelet function: a quenched-flow study

Radiographic contrast media (RCM) may alter platelet behavior at concentrations achieved during cardiac angiography. We used quenched-flow aggregometry coupled to single-particle counting to study the influence of RCM on the kinetics of platelet aggregation (less than 5.0 sec) induced by adenosine diphosphate (ADP, 2.86 microM). At a concentration in platelet-rich plasma (PRP) of 5 per cent RCM by volume, platelet aggregation was inhibited by diatrizoate, iopamidol and ioxaglate either directly or following incubation of each contrast agent with PRP for 20 minutes. Diatrizoate inhibited more than did iopamidol or ioxaglate (56 +/- 6, versus 39 +/- 3 and 40 +/- 9 per cent respectively; P less than 0.003, p less than 0.009, n = 20 normal subjects). A small reduction (about 16 per cent) in aggregation velocity occurred within 5 seconds of exposure of PRP to all 3 RCM and the onset time (t) or lag period before aggregation begins was significantly prolonged by diatrizoate (p less than 0.03). The RCM vehicles alone (iodinated moiety removed, osmolality readjusted) had no effect on the ADP-induced aggregation. Platelet counts fell significantly after incubation with diatrizoate (12%; p = 0.04). Our data therefore show that early platelet aggregation was inhibited by 3 commonly-used ionic and nonionic contrast agents. Inhibition was apparently caused by the iodinated contrast molecule, began within seconds of platelet-RCM contact and was independent of vehicle composition. Since diatrizoate inhibited aggregation more than iopamidol or ioxaglate, its use may be of additional value during angiographic procedures in clinical situations involving enhanced platelet activation.