Clinical Risk Stratification and Use of the Two-level Wells Score

The real value of the D-dimer assay is when it is used appropriately in conjunction with pre-test probability scoring using a risk stratification tool. There are several validated DVT risk stratification tools; the one currently recommended by the National Institute of Clinical Excellence (NICE)⁴ is the Two-level DVT Wells Score shown on the right.⁵

DVT unlikely

Represents low/moderate risk (with a pre-test probability of having a DVT of <15%)⁵ and this score in combination with a negative D-dimer assay results in a 3 month incidence of DVT of approximately 0.5%. This is low enough to pragmatically exclude the diagnosis and discharge the patient.^6,7 A positive D-dimer will require the patient to undergo further imaging.

DVT likely

Represents higher risk (with a pre-test probability of having a DVT of approximately >30%)⁵ before D-dimer testing. Irrespective of the type of assay used, there is no indication for D-dimer in this group because the post-test probability of a negative assay is still too high to exclude the diagnosis. These patients will all require further imaging.

Learning bite

Evidence-based risk stratification is critical to determine appropriate further investigation.