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-characteri zed. The purpose of the present study was to evaluate the sequential e ffects of heparin and then a contrast agent on platelet function durin g an angiographic procedure. Blood samples from 54 patients were obtai ned at baseline, after a 5000 unit bolus of heparin and after administ ration of a contrast agent (iohexol, n=30: diatrizoate, n=24) during a ngiography. The in vitro bleeding time (IVBT) was determined on nonant icoagulated whole blood using a hollow fiber device under physiologica l flow conditions. Mean IVBT at baseline was 3.6 +/- 2.7 minutes and i ncreased to 17.0 +/- 12.3 minutes after heparin (p < 0.01). After hepa rin, 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 pa tients had a large increase in their IVBT. When contrast was given (16 7 +/- 52 mls) following heparin, mean IVBT was higher in those who rec eived diatrizoate (23.3 +/- 9.4 minutes) compared with iohexol (15.0 /- 10.9 minutes, p < 0.05). However, 15 patients (28%) continued to ha ve a normal IVBT after contrast and of these 80% had received iohexol.