The incidence of heparin-induced thrombocytopenia in patients treated with low molecular weight heparin for superficial vein thrombosis

Background: The risk of heparin induced thrombocytopenia ( HIT) associated with low molecular weight heparin (LMWH) for treatment of superficial vein thrombosis (SVT) is uncertain. As a result the necessity of platelet count monitoring is unclear in this setting. Aims: To assess the risk of HIT in outpatients treated with LMWH for SVT. Methods: In a prospective single centre study we included all symptomatic outpatients in whom a real-time B-mode and color Doppler ultrasonography examination revealed SVT without DVT. Patients treated with vitamin K antagonists or fondaparinux were excluded. Patients received full dose enoxaparin for 1 week followed by half therapeutic dose for 3 weeks or parnaparin 8500 UI aXa for 10 days followed by 6400 UI aXa once daily for 20 days. Platelet count was performed on the day of diagnosis (D0) and 7 (D7), and 14 (D14) days afterward. Primary outcomes were the rate of thromboembolic events and of HIT during a 3-month follow-up. Results: 678 outpatients (age: 64.7 +/- 16.2 years, male: 42.0%) were evaluated. During follow-up, 7 venous thrombo-embolic events were recorded (1.03% CI 95%: 0.50-2.11%), while no major bleeding was observed (0.0% CI 95%: 0.0-0.56%). Platelet count was 255 +/- 93 x 10(9)/L at D0, 245 +/- 93 x 10(9)/L at D7 (p = 0.204 vs. D0) and 261 +/- 116 x 10(9)/L at D14 (p = 0.405 vs. D0). No fall in platelet count > 50% and no case of HIT were recorded (HR 0.0% CI 95%: 0-0.56%). Conclusions: A 4-week LMWH treatment for SVT is associated with an incidence of HIT lower than 0.6% and platelet count monitoring may be omitted in this setting.