Ascending venography, although the diagnostic standard for deep vein thrombosis (DVT), has important clinical pitfalls and shortcomings. It is invasive and thus not readily repeated: its use is associated with significant discomfort in many patients and in 3-4% of patients post-veno- graphic phlebitis is induced. A high degree of technical and interpretive skill is required and in up to 20% of patients routine ascending venography fails to visualize the external and common iliac veins. In many hospitals, outpatient access is not readily available necessitating admission to hospital for elective venography. Non-invasive testing with impedance plethysmography (IPG) is gaining increasing acceptance and use because it is objective, versatile and free of morbidity. IPG is sensitive and specific for symptomatic proximal DVT, but has the potential limitation that it is insensitive to calf DVT. Because of this, two different non-invasive approaches are currently advocated: a) serial IPG’s to detect calf vein thrombi which extend proximally (advocates of this approach suggest that calf DVT rarely lead to symptomatic pulmonary emboli unless proximal extension occurs) and b) addition of leg scanning to detect calf DVT. The effectiveness of serial IPG’s is uncertain and to resolve this issue we are currently performing a randomized trial. Multiple large studies however demonstrate that because of both high sensitivity and specificity, the combined approach of IPG and leg scanning provides a replacement for venography in the majority of symptomatic patients. Furthermore, the safety of witholding anticoagulant therapy in patients negative by combined IPG and leg scanning has been confirmed by long-term follow-up. Combined IPG and leg scanning is more cost-effective than elective venography because these non-invasive tests are readily performed in the emergency room or clinic, thus preventing unnecessary admission to hospital of patients with clinically suspected DVT who are negative by testing.
Cost effective strategy for a safe diagnosis of deep vein thrombosis at a district general hospital
