Ultrasound (US) has largely replaced contrast venography as the definitive diagnostic test for deep vein thrombosis (DVT). We aimed to derive a definitive estimate of the diagnostic accuracy of US for clinically suspected DVT and identify study-level factors that might predict accuracy. We undertook a systematic review, meta-analysis and meta-regression of diagnostic cohort studies that compared US to contrast venography in patients with suspected DVT. We searched Medline, EMBASE, CINAHL, Web of Science, Cochrane Database of Systematic Reviews, Cochrane Controlled Trials Register, Database of Reviews of Effectiveness, the ACP Journal Club, and citation lists (1966 to April 2004). Random effects meta-analysis was used to derive pooled estimates of sensitivity and specificity. Random effects meta-regression was used to identify study-level covariates that predicted diagnostic performance. We identified 100 cohorts comparing US to venography in patients with suspected DVT. Overall sensitivity for proximal DVT (95% confidence interval) was 94.2% (93.2 to 95.0), for distal DVT was 63.5% (59.8 to 67.0), and specificity was 93.8% (93.1 to 94.4). Duplex US had pooled sensitivity of 96.5% (95.1 to 97.6) for proximal DVT, 71.2% (64.6 to 77.2) for distal DVT and specificity of 94.0% (92.8 to 95.1). Triplex US had pooled sensitivity of 96.4% (94.4 to 97.1%) for proximal DVT, 75.2% (67.7 to 81.6) for distal DVT and specificity of 94.3% (92.5 to 95.8). Compression US alone had pooled sensitivity of 93.8 % (92.0 to 95.3%) for proximal DVT, 56.8% (49.0 to 66.4) for distal DVT and specificity of 97.8% (97.0 to 98.4). Sensitivity was higher in more recently published studies and in cohorts with higher prevalence of DVT and more proximal DVT, and was lower in cohorts that reported interpretation by a radiologist. Specificity was higher in cohorts that excluded patients with previous DVT. No studies were identified that compared repeat US to venography in all patients. Repeat US appears to have a positive yield of 1.3%, with 89% of these being confirmed by venography. Combined colour-doppler US techniques have optimal sensitivity, while compression US has optimal specificity for DVT. However, all estimates are subject to substantial unexplained heterogeneity. The role of repeat scanning is very uncertain and based upon limited data.

/pdf/systematic-review-and-meta-analysis-of-the-diagnostic-2pqsbtlf4h.pdf

Systematic review and meta-analysis of the diagnostic accuracy of ultrasonography for deep vein thrombosis

The authors summarized published research on the sensitivity and specificity of clinical findings, risk scores, and physicians' empirical judgments for deep venous thrombosis (DVT). Only malignancy...

Meta-Analysis: The Value of Clinical Assessment in the Diagnosis of Deep Venous Thrombosis

Objectives: 

To estimate the diagnostic accuracy of
non-invasive tests for proximal deep vein thrombosis
(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. Also to identify practical diagnostic
algorithms for DVT, and estimate the diagnostic
accuracy, clinical effectiveness and cost-effectiveness
of each.


Data sources: 

Electronic databases (to April 2004).
A postal survey of hospitals in the UK.

Review methods: 

Selected studies were assessed
against validated criteria. A postal survey of hospitals in
the UK was undertaken to describe current practice
and availability of tests, and identify additional
diagnostic algorithms. Pooled estimates of sensitivity,
specificity and likelihood ratios were obtained for each
test using random effects meta-analysis. The effect of
study-level covariates was explored using random
effects metaregression. A decision-analytic model was
used to combine estimates from the meta-analysis and
estimate the diagnostic performance of each algorithm
in a theoretical population of outpatients with
suspected DVT. The net benefit of using each algorithm
was estimated from a health service perspective, using
cost–utility analysis, assuming thresholds of willingness
to pay of £20,000 and £30,000 per quality-adjusted lifeyear
(QALY). The model was analysed probabilistically
and cost-effectiveness acceptability curves were
generated to reflect uncertainty in estimated costeffectiveness.


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 costeffective
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: 

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 among the most 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. Recommendations for research include the
evaluation of the costs and outcomes of using the
optimal diagnostic algorithms in routine practice, the
development and evaluation of algorithms appropriate
for specific groups of patients with suspected DVT,
such as intravenous drug abusers, pregnant patients and
those with previous DVT, the evaluation of the role of
plethysmography: interaction with other diagnostic
tests, outcome of low-risk patients with negative
plethysmography and measurement of the costs of
providing plethysmography, and methodological
research into the incorporation of meta-analytic data
into decision-analytic modelling.

Measurement of the clinical and cost-effectiveness of non-invasive diagnostic testing strategies for deep vein thrombosis.

Objective To summarise the evidence supporting the use of rapid D-dimer testing combined with estimation of clinical probability to exclude the diagnosis of deep venous thrombosis among outpatients. Data sources Medline (June 1993 to December 2003), the Database of Abstracts and Reviews (DARE), and reference lists of studies in English. Selection of studies We selected 12 studies from among 84 reviewed. The selected studies included more than 5000 patients and used a rapid D-dimer assay and explicit criteria to classify cases as having low, intermediate, or high clinical probability of deep vein thrombosis of the lower extremity among consecutive outpatients. Review methods Diagnosis required objective confirmation, and untreated patients had to have at least three months of follow up. The outcome was objectively documented venous thromboembolism. Two authors independently abstracted data by using a data collection form. Results When the less sensitive SimpliRED D-dimer assay was used the three month incidence of venous thromboembolism was 0.5% (95% confidence interval 0.07% to 1.1%) among patients with a low clinical probability of deep vein thrombosis and normal D-dimer concentrations. When a highly sensitive D-dimer assay was used, the three month incidence of venous thromboembolism was 0.4% (0.04% to 1.1%) among outpatients with low or moderate clinical probability of deep vein thrombosis and a normal D-dimer concentration. Conclusions The combination of low clinical probability for deep vein thrombosis and a normal result from the SimpliRED D-dimer test safely excludes a diagnosis of acute venous thrombosis A normal result from a highly sensitive D-dimer test effectively rules out deep vein thrombosis among patients classified as having either low or moderate clinical probability of deep vein thrombosis.

https://www.bmj.com/content/bmj/329/7470/821.full.pdf

Combined use of rapid D-dimer testing and estimation of clinical probability in the diagnosis of deep vein thrombosis: systematic review.

Background: Numerous studies have evaluated the accuracy of D-dimer in diagnosing suspected deep vein thrombosis (DVT), but results are conflicting.

Aim: To overview estimates of the diagnostic accuracy of D-dimer and identify causes of variation.

Design: Systematic review, meta-analysis and meta-regression.

Methods: We searched Medline, EMBASE, CINAHL, Web of Science, Cochrane Database of Systematic Reviews, Cochrane Controlled Trials Register, Database of Reviews of Effectiveness, the ACP Journal Club, citation lists, and contacted manufacturers. We selected studies that compared D-dimer to a reference standard in patients with suspected DVT. Data were analysed by random effects meta-analysis and meta-regression.

Results: We included 97 studies reporting 198 assays in 99 different patient groups. Overall estimated sensitivity and specificity of D-dimer were 90.5% and 54.7%, but both estimates were subject to significant heterogeneity ( p < 0.001). Meta-regression identified that some heterogeneity was explained by study setting, exclusion criteria, whether recruitment was consecutive or the study prospective, whether D-dimer and the reference standard were measured blind, and whether the D-dimer threshold was determined a priori . Sensitivity and specificity also varied between ELISA (94% and 45% respectively), latex (89% and 55%) and whole blood agglutination assays (87% and 68%). Sensitivity was higher for proximal than distal DVT. Specificity was dependent upon whether clinical probability of DVT was high (specificity 51%), intermediate (67%) or low (78%).

Discussion: D-dimer has good sensitivity, but poor specificity, for DVT. Estimates are subject to substantial heterogeneity from various sources. D-dimer specificity appears to be strongly dependent upon the pre-test clinical probability of DVT.

/pdf/variation-in-the-diagnostic-performance-of-d-dimer-for-4mmrgc8dyp.pdf

Variation in the diagnostic performance of D-dimer for suspected deep vein thrombosis

The aim was to show that clinical assessment and serial Dopplers could be used to exclude deep venous thrombosis (DVT), and also that clinical assessment in combination with D-dimers could be used to exclude DVT. This was a prospective trial. Patients underwent clinical assessment, colour flow Doppler, and D-dimer measurement. Patients with an equivocal first Doppler and patients with a moderate/high pre-test clinical score had a repeat Doppler. Follow up information was obtained to see if further thromboembolism developed. Outcome measures included the reliability of the clinical assessment, Doppler, and D-dimer in excluding DVT. One hundred and ninety four patients were enrolled. The negative predictive value of a low medical pre-test score in excluding DVT was 92%. Eighty eight patients underwent D-dimer measurement. The negative predictive value of a D-dimer <400 units was 96%. The negative predictive value of a low clinical pre-test score and D-dimer <400 units was 100%. The negative predictive value of a low clinical pre-test score and D-dimer <800 units was 97%. The negative predictive value of the combination of a low clinical pre-test score and D-dimer <400 units was 100%. Twenty three per cent of patients had a low clinical pre-test score and D-dimer <400 units. Thus, a DVT could be excluded in 23% of referred patients. This information could be used to reduce Doppler requests by 23%. No patient in whom clinical assessment and serial Dopplers had excluded a DVT suffered further thromboembolism on follow up. This study has thus shown that a low medical pre-test score and negative Doppler reliably exclude DVT; a low pre-test score and negative D-dimer would reliably exclude DVT.

https://pmj.bmj.com/content/postgradmedj/78/926/742.full.pdf

An algorithm for the investigation and management of patients with suspected deep venous thrombosis at a district general hospital

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An algorithm for the investigation and management of patients with suspected deep venous thrombosis at a district general hospital