Background

A wide range of diagnostic tests may be useful in diagnosing deep vein thrombosis (DVT), including clinical assessment, D-dimer, plethysmography, rheography, ultrasound, computed tomographic (CT) scanning, magnetic resonance imaging (MRI) and venography. These may be used in isolation or combined as an algorithm.

Objectives

The objectives of the study were:

• To estimate the diagnostic accuracy of non-invasive tests for proximal DVT and isolated calf DVT, in patients with clinically suspected DVT or high-risk asymptomatic patients, and identify factors associated with variation in diagnostic performance.
• To identify practical diagnostic algorithms for DVT, and estimate the diagnostic accuracy, clinical effectiveness and cost-effectiveness of each.

Methods

Results

Individual clinical features are of limited diagnostic value, with most likelihood ratios being close to 1. Wells clinical probability score stratifies proximal, but not distal, DVT into high-, intermediate- and low-risk categories. Unstructured clinical assessment by experienced clinicians may have similar performance to Wells score. In patients with clinically suspected DVT, D-dimer has 91% sensitivity and 55% specificity for DVT, although performance varies substantially between assays and populations. D-dimer specificity is dependent on pretest clinical probability, being higher in patients with a low clinical probability of DVT. Plethysmography and rheography techniques have modest sensitivity for proximal DVT, poor sensitivity for distal DVT, and modest specificity. Ultrasound has 94% sensitivity for proximal DVT, 64% sensitivity for distal DVT and 94% specificity. Computed tomography scanning has 95% sensitivity for all DVT (proximal and distal combined) and 97% specificity. Magnetic resonance imaging has 92% sensitivity for all DVT and 95% specificity. The diagnostic performance of all tests is worse in asymptomatic patients.

The most cost-effective algorithm discharged patients with a low Wells score and negative D-dimer without further testing, and then used plethysmography alongside ultrasound, with venography in selected cases, to diagnose the remaining patients. However, the cost-effectiveness of this algorithm was dependent on assumptions of test independence being met and the ability to provide plethysmography at relatively low cost. Availability of plethysmography and venography is currently limited at most UK hospitals, so implementation would involve considerable reorganisation of services.

Two algorithms were identified that offered high net benefit and would be feasible in most hospitals without substantial reorganisation of services. Both involved using a combination of Wells score, D-dimer and above-knee ultrasound. For thresholds of willingness to pay of £10,000 or £20,000 per QALY the optimal strategy involved discharging patients with a low or intermediate Wells score and negative D-dimer, ultrasound for those with a high score or positive D-dimer, and repeat scanning for those with positive D-dimer and a high Wells score, but negative initial scan. For thresholds of £30,000 or more a similar strategy, but involving repeat ultrasound for all those with a negative initial scan, was optimal.

Conclusions

Publication

• Goodacre S, Sampson F, Stevenson M, Wailoo A, Sutton A, Thomas S, et al. Measurement of the clinical and cost-effectiveness of non-invasive diagnostic testing strategies for deep vein thrombosis. Health Technol Assess 2006;10(15). [PubMed: 16707072]

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