THE INCIDENCE OF HEPARIN-INDUCED ANTIBODIES IN PATIENTS UNDERGOING VASCULAR-SURGERY - A PROSPECTIVE-STUDY

Purpose: This study prospectively assessed the incidence of heparin-in duced antibodies in patients undergoing peripheral vascular surgery an d determined whether the incidence is influenced by previous heparin e xposure. Methods: Fifty-four hospitalized patients (36 men and 18 wome n) undergoing peripheral vascular surgery and receiving intraoperative heparin anticoagulation were studied. Unfractionated porcine heparin was given for intraoperative anticoagulation and was not continued pos toperatively. Carotid endarterectomy was performed in 36 patients, aor tic reconstruction in II patients, and infrainguinal bypass in 7 patie nts. Plasma was tested before and after (14 +/- 7.5 [SD] days) surgery for IgG antibodies to the complex of heparin/platelet factor 4, using a standardized, validated enzyme-linked immunosorbent assay (ELISA). Results are expressed as an optical density ratio (ODR) of patient pla sma to normal plasma, with the threshold for a positive result of grea ter than or equal to 1.8. Platelet counts and clinical outcomes were a lso assessed. Results: The mean patient age was 67.2 +/- 9.7 years. A prior exposure to heparin was documented in 41% of patients. The mean intraoperative heparin dose was 9089 +/- 3607 units. Only I patient co nverted from a negative antibody status to a positive status (1.9%, 95 % CI = 0.10% - 11.18%). The change in the ELISA ODR after surgery was not significantly different for patients with (+0.042 +/- 0.272) and w ithout (-0.022 +/- 0.299, P = 0.57) prior heparin exposure. Postoperat ively, the platelet counts dropped from 227,620 +/- 78,308 mu L, to 18 5,706 +/- 80,842 mu L (P < .001). The decrease in platelet count was t he same in patients with prior heparin exposure (-23.0 +/- 18.0%) and without (-18.0 +/- 14.0%, P = .46). One thrombotic complication occurr ed, a femorotibial bypass graft occlusion in a patient who tested nega tive for antibodies. Conclusion: Heparin-induced antibodies occur infr equently after peripheral vascular surgery. The commonly observed, mil d degree of postoperative thrombocytopenia does not appear to be cause d by heparin-induced antibodies. These results indicate that a standar d dose of heparin for intraoperative anticoagulation during vascular s urgery is not associated with a significant risk of heparin-induced th rombocytopenia and thrombosis.