Multislice CT scans can detect pulmonary embolisms without ultrasonography of the leg

April 17, 2008

Using D-dimer measurement* combined with multislice CT scan** (MSCT) to detect pulmonary embolism***(PE) is as effective as using D-dimer, venous ultrasonography of the leg and MSCT. Thus, venous ultrasonography is no longer needed for the diagnostic strategy of PE when MSCT is used. These are the conclusions of authors of an Article in this week's edition of The Lancet.

Contemporary diagnostic methods to detect PE include clinical probability assessment (CPA) followed by sequential diagnostic tests, such as D-dimer, ultrasonography and CT scans. CT of the chest has emerged as a new way to directly visualise the clot in the pulmonary arteries, however first-generation 'single slice' CT had a low sensitivity (around 70%) for detecting PE â€" restricting its use as a stand alone test. Emergence of MSCT has renewed hope that it could replace pulmonary angiography because of better visualisation of the segmental and subsegmental vessels.

Dr Marc Righini, Geneva University Hospital and Faculty of Medicine, Switzerland, and colleagues did a randomised controlled trial of 1819 outpatients with clinically suspected PE, comparing two strategies. The first (903 patients) assessed CPA combined with D-Dimer measurement and MSCT. The second strategy (916 patients) was the same as the first but included venous ultrasonography of the leg. Effectiveness of each method was assessed by calculating the 3-month risk of recurrent deep vein thrombosis or PE in patients who were left untreated on the basis of having been excluded by either strategy.

The researchers found that the prevalence of PE was 20.6% in both groups -- 186 in the DD-CT group, and 189 in DD-CT-US group. After exclusion of these patients, 838 patients remained in the DD-CT group, and 855 in the DD-US-CT group. Analysis of these patients showed that the 3-month risk of PE was 0.3% in both groups, ie, both strategies were equally effective. The authors say that, compared with old method of doing lung scans (requiring nuclear medicine techniques) MSCT will be easy to do and widely available to physicians.

The authors say: "We conclude that ultrasound is not needed to rule out pulmonary embolism when MSCT is used. An ultrasound could be of use in patients with a contraindication to CT." Dr Righini discusses the paper in this week's Lancet podcast, available Friday on

In an accompanying Comment, Professor Paul Kyrle and Professor Sabine Eichinger, Medical University of Vienna, say: "This approach will facilitate the diagnostic work-up of patients with suspected pulmonary embolism and seems to be cost-effective." They also discuss some new treatments for PE currently in phase III clinical trials.
Notes to editors:

* D-dimer is a fibrin degradation product, a small protein fragment present in the blood after a blood clot is degraded by the body's natural processes (fibrinolysis), and can thus be used to diagnose thromboembolism.

**MSCT (Multislice computed tomography) scanner: A CT scanner in which many detectors rotate around the patient.

***pulmonary embolism: a blockage of the pulmonary artery (or one of its branches), usually when a venous thrombus (blood clot from a vein), becomes dislodged from its site of formation and embolizes to the arterial blood supply of one of the lungs. This process is termed thromboembolism.



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