"Exclusion of deep vein thrombosis using the Wells rule in clinically important subgroups: individual patient data meta-analysis"
BMJ
http://www.bmj.com/content/348/bmj.g366/rr/689698
"Conclusion Combined with a negative D-dimer test result (both quantitative and qualitative), deep vein thrombosis can be excluded in patients with an unlikely score on the Wells rule. This finding is true for both sexes, as well as for patients presenting in primary and hospital care. In patients with cancer, the combination is neither safe nor efficient. For patients with suspected recurrent disease, one extra point should be added to the rule to enable a safe exclusion."