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Algorithm reliable, safe for diagnostic management of DVT
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An algorithm that combines whole-leg and limited compression ultrasonography appeared to be a reliable and safe tool for the diagnostic management of patients with clinically suspected deep vein thrombosis, according to findings from the PALLADIO study.
“The diagnostic algorithm has the potential to safely rule out venous thrombosis on the day of referral in all patients, obviating the inconvenience of repeat testing and reducing the risk of overdiagnosis of low-risk, isolated, distal DVT,” Walter Ageno, MD, of the department of clinical and experimental medicine at University of Insubria in Varese, Italy, and colleagues wrote.
Compression ultrasonography is standard in the assessment of patients with clinically suspected DVT. Whole-leg compression ultrasonography — which is extended to the entire deep venous system — is advantageous because it is conclusive after one test; however, it requires a trained operator and costly scanners. The scan may also increase the risk for potentially unnecessary anticoagulation by detecting isolated thrombi below the knee that may not be clinically significant.
Limited compression ultrasonography — which is restricted to the proximal veins only — is simpler, faster, more reproducible and widely available. However, initial negative results require a repeat ultrasonography within a week, unless DVT was excluded by additional tests.
As such, Ageno and colleagues sought to assess the diagnostic value of an algorithm that would combine both approaches.
The analysis included data from 1,162 patients aged at least 18 years who were outpatients with suspected DVT. Patients underwent D-dimer measurement and a pretest clinical probability assessment.
If the pretest probability was unlikely and D-dimer was negative, DVT was ruled out in patients without additional testing (group 1, n = 351). Patients who had a likely pretest probability or positive D-dimer underwent limited compression ultrasonography alone (group 2, n = 401). Patients with a likely pretest probability and positive D-dimer underwent extended whole-leg compression ultrasonography (group 3, n = 410).
The primary outcome was the incidence of venous thromboembolism.
The algorithm detected DVT in 1,162 (18%) patients, including 12 (3%) from group 2 and 200 (49%) from group 3.
Of all the detected thrombi in group 3, 118 were proximal and 82 were isolated distal thromboses. Thus, 7% of patients in the entire study cohort (82 of 1,162) were diagnosed with isolated distal DVT with the algorithm. Thirty-nine percent of DVT detected (82 of 212) were isolated distal DVT.
Researchers followed the 950 patients for whom the algorithm ruled out DVT for 3 months.
Because there were 26 protocol violations, 351 patients in group 1, 371 patients in group 2 and 202 patients in group 3 who were excluded by the algorithm were included in the analysis at 3 months. Overall, there were eight DVTs reported — one in the first group, four in the second group and three in the third group.
The 3-month incidence of VTE in untreated patients following a negative diagnostic approach was 0.87% (95% CI, 0.44-1.7).
“Our results indicate that, in patients negative for D-dimer and with an unlikely pretest clinical probability of DVT, it is safe to withhold objective imaging testing,” Ageno and colleagues wrote. “In this group of patients, the incidence of VTE during 3-month follow-up was negligible. Furthermore, in patients with either a positive D-dimer test or a likely pretest probability of DVT, our findings suggest it is safe to restrict the ultrasound assessment to the proximal vein system, with no need for repeat testing.”
The researchers identified a lack of a control group, exclusion of patients with previous thrombosis in the index leg, and use of different D-dimer assays as possible limitations to these findings.
Further, seven patients in group 2 were excluded from the analysis because they requested a repeat ultrasound assessment — despite having DVT ruled out after limited compression ultrasonography — and received anticoagulant treatment. If they were included, the incidence rate of VTE would have increased to 1.41% (95% CI, 0.82-2.39), which would have made the upper limit of the 95% CI surpass the 2% cutoff in the study design.
Still, implementation of this stratified approach in clinical practice is warranted, according to the researchers.
“Our integrated strategy allows prompt, safe and convenient management of symptomatic patients while simultaneously confining assessment of the below-knee venous system to a fairly small proportion of patients, identified by pretest probability and D-dimer as being at high risk for DVT,” Ageno and colleagues concluded. – by Anthony SanFilippo
Disclosure: The researchers report no relevant financial disclosures.
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