Wells score

The Wells score is a simple checklist that turns a doctor's bedside impression into a number, estimating how likely a pulmonary embolism is before any blood test or scan. It is like a weather forecast for a diagnosis: it does not confirm rain, but it tells you how worried to be and what to do next.

The score adds up points for clinical clues such as signs of a leg clot, a heart rate above 100, recent surgery or immobility, a previous clot, coughing up blood, and the clinician's judgement that pulmonary embolism is the most likely diagnosis. The total places the patient into a probability category, low or high in the simplified two-level version, which then guides whether to start with a D-dimer or go straight to imaging.

Crucially, the Wells score is a triage tool, not a diagnosis. A low score combined with a normal D-dimer can safely exclude pulmonary embolism without a scan, whereas a high score usually warrants CT pulmonary angiography regardless of D-dimer. It works best applied consistently to the kind of patients in whom it was validated, and clinical judgement still overrides the number when the picture is unusual.