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 × 109/L at D0, 245 ± 93 × 109/L at D7 (p = 0.204 vs. D0) and 261 ± 116 × 109/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.