A randomized management study of impedance plethysmography vs. contrast venography in patients with a first episode of clinically suspected deep veinthrombosis

Objectives: In this randomized management study, we examined the safety of withholding anticoagulation on the basis of negative impedance plethysmogra phy (IPC) compared to negative contrast venography (CV) in symptomatic pati ents with a first episode of clinically suspected deep vein thrombosis (DVT ), and we determined the impact of the limitations of IPG or CV on their cl inical utility. Methods: Patients at a university teaching hospital present ing with a first episode of clinically suspected DVT were randomized to one of two management strategies at study entry: (1) IPG: if positive, confirm atory CV was performed. If CV was positive, anticoagulants were administere d, if CV was negative, anticoagulants were held. If negative, IPC was repea ted serially and if it remained negative, anticoagulants were held (n = 165 ). (2) CV: if positive, anticoagulants were administered, if negative, anti coagulants were held (n=159). The negative predictive value (NPV) of IPC an d CV, positive predictive value (PPV) of IPG, and the failure rate of each strategy were assessed. Results: Among IPG patients, 28 of 37 with positive IPG initially or during serial testing and evaluable CV had confirmed DVT (PPV 76%; 95% confidence interval, CI [62%, 90%]). DVT was diagnosed during serial testing in 2.1% of patients with initially negative IPC who complet ed testing. The NPV overall of negative IPG was 98.3%. During follow-up, tw o patients in the IPC group (1.2%) and two patients in the CV group (1.3%) developed venous thromboembolism (VTE). Death during follow-up occurred in 11% of IPG patients compared to 6% of CV patients (P=.13) The investigation strategy failed in 25% of IPG patients and in 14% of CV patients. Conclusi ons: Our findings demonstrate that the two diagnostic strategies we studied are equivalent methods for ruling out DVT in patients with a first episode of suspected DVT. The PPV of IPG was too low to permit its use alone as a test to rule in DVT. Both strategies had surprisingly high failure rates. ( C) 2001 Elsevier Science Ltd. All rights reserved.