Is all well with the Wells score?

Dr Philip White, medicolegal consultant at Medical Protection, looks at a common cause of claims – missed diagnosis of deep vein thrombosis

The Wells criteria is a clinical scoring process used in the diagnosis of acute pulmonary embolism (PE) and deep vein thrombosis (DVT).

Medical Protection regularly pays out significant compensation to patients when their GP misses the diagnosis of lower limb DVT (deep vein thrombosis). They are frequently very distressing cases as the diagnosis is often made at post-mortem examination after a PE (pulmonary embolus) has occurred, and it is often in young adults. In many cases at Medical Protection, the missed diagnosis has occurred where clinicians misinterpret how to use the Wells score.

Case studies

1. A 40-year-old man played squash, felt a bit of a twinge in his calf and saw his GP a couple of days later, as his calf had slightly swelled up. The GP and the patient both thought a sprain was likely. The Wells score was calculated at -2 so a d-dimer was not needed; the patient was reassured there was no DVT.
2. A 38-year-old woman had just come back from Spain with a slight pain in her calf. There was nothing to find on examination but she was worried because her friend had previously had DVT. The Wells score was 0 and it didn’t look like a DVT, so d-dimer was not needed and the patient was reassured that it was not DVT.

So far so good.

Wells score (1997)

If a DVT is considered, the Wells score is calculated this way:

• Active cancer (treatment ongoing or within six months, or palliative) +1 point
• Paralysis, paresis, recent immobilisation of the lower limbs +1 point
• Recently bedridden for >3 days, or major surgery within four weeks +1 point
• Localised tenderness along distribution of deep venous system +1 point
• Entire leg swelling +1 point
• Calf swelling >3 cm, compared with asymptomatic leg +1 point
• Pitting oedema (greater in symptomatic leg) +1 point
• Collateral superficial veins (non-varicose) +1 point
• Alternative diagnosis as likely, or more likely, than DVT −2 points

Modified Wells score (2003)

Scoring criteria as for Wells score, with the addition of:

• Previous documented DVT +1 point

Interpretation

Wells score ≥3 = high, 1-2 = moderate, 0 = low probability

Modified Wells score ≥2 = likely DVT, <2 = DVT unlikely

Note: there have been multiple revisions of both the Wells criteria for DVT and the Wells criteria for Pulmonary Embolisms. Be sure to stay up-to-date with any amendments to the Wells score methods.

Conclusion: Not all well with the Wells score

In the scenarios above, the clinicians used the low Wells score to reassure them that a DVT was unlikely so the d-dimer test was not needed. However, this is exactly the situation where it is needed. D-dimer is a ‘rule out’ test that’s recommended to exclude a DVT where you already think there probably isn’t one (Wells score <2). If it really looks like it could be a DVT (Wells score >3), forget the d-dimer and go straight for a scan.

Even if you think you’ve got it covered, why not audit the d-dimers or swollen legs at your practice or out of hours clinic, to make sure everybody else has? 

Follow Dr Philip White on Twitter: @philiptwhite