Meta-analysis1 of individual patient data included 13 studies with a total of 10 002 outpatient subjects with suspected deep vein thrombosis. Increasing scores on the Wells rule were associated with an increasing probability of having deep vein thrombosis. Estimated probabilities were almost twofold higher in patients with cancer and in patients with suspected recurrent events.
The probability of deep vein thrombosis in patients with an unlikely Wells rule score (≤1) combined with a negative D-dimer test result was low (1.2%, 95% CI 0.7% to 1.8%), enabling exclusion of about one in three suspected patients (Wells ≤1 with a negative D-dimer test occurred in 29% of the patients). This finding was consistent in subgroups defined by sex, care setting (primary versus hospital), and type of D-dimer assay (qualitative versus quantitative).
In patients with cancer, the combination was neither safe nor efficient: Wells score ≤ 1 combined with a negative D-dimer test occurred in 9% of patients with cancer and was associated with a 2.2% probability of deep vein thrombosis.
For patients with suspected recurrent deep vein thrombosis, use of the original Wells rule was not safe (failure rate 2.5%, 95% CI 1.2 to 5.4). Adding one point to the original Wells score in patients with a history of deep vein thrombosis (the updated model), and defining low risk as a score ≤1 combined with a negative D-dimer test result leaded to a failure rate of 1.0% (95% CI 0.6% to 1.6%) enabling the safe exclusion of deep vein thrombosis in suspected patients.
Comment: Given that even invasive venography cannot find all cases, a failure of up to 2% is often deemed as acceptable.
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