Systematic review of non-invasive diagnostic tests for deep vein thrombosis
Project title:
Measurement of the clinical and cost effectiveness of non invasive diagnostic testing strategies for deep vein thrombosis
Funder:
Department of Health Research and Development Health Technology Assessment Programme
Project staff:
- Steve Goodacre, lead investigator
- Fiona Sampson, project manager
- Kathryn Paulucy, clerical officer
Outline of project design:
- Systematically review the literature and undertake meta-analysis to estimate the diagnostic accuracy of clinical assessment and non invasive diagnostic tests for deep vein thrombosis
- Survey current practice, systematically review the literature and undertake decision analysis modelling to identify appropriate diagnostic algorithms that combine these tests
- Use economic modelling to estimate the cost per quality-adjusted year of life gained by each algorithm
Project objectives:
- To measure the diagnostic accuracy of clinical assessment, D-dimer, ultrasonography, impedance plethysmography, magnetic resonance imaging (MRI) and computer tomographic (CT) scanning for- a) proximal, and b) isolated calf DVT
- To develop feasible algorithms for the diagnosis of DVT involving combinations of clinical assessment and non invasive diagnostic tests and measure the diagnostic accuracy of each algorithm.
- To assess the utility of diagnostic strategies in terms that are clinically relevant and important and explore the relationship between anatomical site of DVT or venographic findings, and clinically relevant outcomes
- To measure the incremental cost per quality-adjusted year of life (QALY) gained by each diagnostic algorithm compared to the next most effective alternative
- To explore the consistency of findings in different patient groups, different settings and for different baseline prevalences of DVT
- To determine what further empirical data is required to increase the reliability of estimates.
Findings
Conclusions
Diagnostic algorithms based on a combination of Wells score, D-dimer and ultrasound (with repeat if negative) are feasible at most UK hospitals and are cost-effective. Use of repeat scanning depends on the threshold for willingness to pay for health gain. Further diagnostic testing for patients with a low Wells score and negative D-dimer is unlikely to represent a cost-effective use of resources.
Clinical signs
Individual clinical features are of limited diagnostic value. 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.
D-dimer
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
Plethysmography and rheography techniques have modest sensitivity for proximal DVT, poor sensitivity for distal DVT, and modest specificity. As with clinical signs and D-dimer, it may play a role within diagnostic testing algorithms but not alone.
Ultrasound, CT & MRI
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. CT and MRI offer a useful alternative in patients for whom ultrasound is not possible.
Cost-effectiveness of algorithms
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.
Outputs
The HTA report was published in 2006 (see 'see also' box). We have published a number of journal articles, which are all accessible from the 'publications' box at the top of this page. Conference abstracts can be downloaded from the downloads box