Diagnosis of deep venous thrombosis and alternative diseases in symptomatic outpatients

BACKGROUND: The management of patients with suspected deep vein thrombosis (DVT) is controversial. Recent studies have suggested that anticoagulant treatment can safely be withheld if the clinical probability is low and the D-dimer concentration in blood is normal. We examined a diagnostic algorithm comparing a score-based, explicit assessment model with our empirical, implicit approach, which was designed to be more sensitive for distal DVT. We further investigated what information would be lost by not performing a routine ultrasound examination in each patient. METHODS: Consecutive patients with suspected DVT first received a D-dimer estimation, then an examination to assess the clinical probability, and ultimately objective testing for DVT or alternative diseases. Ultrasound was used in all patients; venography and other tests were performed as indicated. The implicit assessment of clinical probability was compared with the explicit scoring system of Wells et al., and the value of ultrasound was assessed retrospectively. RESULTS: In 57 of 206 patients (28%), DVT was confirmed. A high clinical probability was attributed to all pelvic and femoral DVT (except one), but popliteal and crural DVT were missed in 78% by the explicit approach and in 34% by the implicit approach. The negative predictive values for any DVT were 83% for the explicit assessment and 92% for the implicit assessment, 95% for the D-dimer estimation, and 98% (95% CI 92-99) for the combination of low implicit clinical probability and a negative D-dimer test. This combination yielded the same NPV for isolated crural DVT and was found in 41% of all suspected cases. An alternative organic diagnosis was established in 100 patients (48%) and no organic diagnosis was made in 49 (24%). In half of all suspected cases, irrespective of whether DVT was present or not, concomitant or alternative venous pathologies were observed. Ultrasound was found useful in 91% of cases. CONCLUSIONS: Proximal as well as distal DVT can reliably be excluded when both a sensitive assessment of clinical probability and a bedside D-dimer assay are negative. Nevertheless, ultrasound is helpful in establishing alternative diagnoses. Strategies to reduce the number of ultrasound investigations appear to lack comprehensiveness.