Evaluating the Use of a Negative D-Dimer and Modified Low Wells Score in Excluding above Knee Deep Venous Thrombosis in an Outpatient Population, Assessing Need for Diagnostic Ultrasound
Aims. Colour doppler ultrasonography (CDUS) is widely used in the diagnosis of deep venous thrombosis (DVT); however, the number of scans positive for above knee DVT is low. The present study evaluates the reliability of the D-dimer test combined with a clinical probability score (Wells score) in ruling out an above knee DVT and identifying patients who do not need a CDUS. Materials and Method. This study is a retrospective audit and reaudit of a total of 816 outpatients presenting with suspected lower limb DVT from March 2009 to March 2010 and from September 2011 to February 2012. Following the initial audit, a revised clinical diagnostic pathway was implemented. Results. In our initial audit, seven patients (4.9%) with a negative D-dimer and a low Wells score had a DVT. On review, all seven had a risk factor identified that was not included in the Wells score. No patient with negative D-dimer and low Wells score with no extra clinical risk factor had a DVT on CDUS (negative predictive value 100%). A reaudit confirmed adherence to our revised clinical diagnostic pathway. Conclusions. A negative D-dimer together with a low Wells score and no risk factors effectively excludes a lower limb DVT and an ultrasound is unnecessary in these patients. 1. Introduction Deep venous thrombosis (DVT) is a common cause of mortality and morbidity with an estimated incidence of 67 per 100？000 general populations per year [1] and a cumulative lifetime incidence of 2 to 5% [2]. Accurate diagnosis of DVT is necessary because untreated DVT can result in thromboembolic disease and misdiagnosis is associated with bleeding due to the treatment with anticoagulants [3]. Diagnosis of DVT is made by varying combinations of history, physical examination, clinical probability score, blood test for D-dimer, and compression ultrasonography (CDUS). Among the patients who are referred for scanning with suspected DVT, less than 25% have the disease [4]. Over the past decades, the clinical diagnostic methods have developed considerably; however, the accurate tests are costly and the cheap ones are not reliable [5]. CDUS is still the initial approach in the diagnosis of DVT in many centres [6, 7]. It is a reliable and accurate diagnostic test to confirm or rule out DVT, but since only 17% to 24% of suspected patients have a DVT, it is not appropriate and cost-effective to request this investigation in all patients [8, 9]. Numerous studies demonstrate that a combination of a clinical probability assessment (e.g., Wells score), D-dimer, and CDUS might be a reliable means of excluding
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