Variable influence of heparin and contrast agents on platelet function as assessed by the in vitro bleeding time

Both heparin and contrast agents have anticoagulant effects which are well-documented but their effects on platelets are not well-characterized. The purpose of the present study was to evaluate the sequential effects of heparin and then a contrast agent on platelet function during an angiographic procedure. Blood samples from 54 patients were obtained at baseline, after a 5000 unit bolus of heparin and after administration of a contrast agent (iohexol, n = 30: diatrizoate, n = 24) during angiography. The in vitro bleeding time (IVBT) was determined on nonanticoagulated whole blood using a hollow fiber device under physiological flow conditions. Mean IVBT at baseline was 3.6 +/- 2.7 minutes and increased to 17.0 +/- 12.3 minutes after heparin (p < 0.01). After heparin, 44.5% of the patients still had a normal IVBT (< 9.0 minutes), 11% of the patients had a moderately increased IVBT and the remaining patients had a large increase in their IVBT. When contrast was given (167 +/- 52 mls) following heparin, mean IVBT was higher in those who received diatrizoate (23.3 +/- 9.4 minutes) compared with iohexol (15.0 +/- 10.9 minutes, p < 0.05). However, 15 patients (28%) continued to have a normal IVBT after contrast and of these 80% had received iohexol.