Accuracy and usefulness of a clinical prediction rule and D-dimer testing in excluding deep vein thrombosis in cancer patients

Introduction: Deep vein thrombosis (DVT) can be safety and reliably excluded in patients with a low clinical probability and a negative D-dimer result but the accuracy and utility of such a strategy is less certain in cancer patients. We sough to compare the performance of the Wells pretest probability (PTP) model and D-dimer testing between patients with and without cancer and to examine the utility of the two PTP model classification schemes (low/moderate/high versus unlikely/likely) in excluding DVT in patients with cancer. Materials and methods: Pooled analysis of databases from three prospective diagnostic studies evaluating consecutive outpatients with suspected DVT. Results: A total of 2696 patients were evaluated. DVT was diagnosed in 403 (15%) patients overall and in 83 of 200 (41.5%) cancer patients. The PTP distribution and the prevalence of DVT in each PTP category were significantly different between patients with and without cancer, regardless of the classification used (p<0.01). In patients with cancer, the negative predictive values of a low or unlikely PTP score in combination with a negative D-dimer result were 100% (95% CI 69.8%-100%) and 100% (95% CI 82.8%-96.6%), respectively. However, the specificities ranged from 46.2% (95%CI 27.1%-66.3%) to 57.1% (95%CI 41.1%-71.9%). Further testing was required in 94% of cancer patients using the low/moderate/high PTP classification and in 88% using the unlikety/likely stratification. Conclusions: As in patients without cancer, the combination of a low or unlikely PTP with a negative D-dimer result can exclude DVT in patients with cancer. However, this strategy has limited utility because very few cancer patients present with this combination. (C) 2008 Elsevier Ltd. All rights reserved.