Wells score (pulmonary embolism)

The Wells score is a clinical prediction rule used to classify patients suspected of having pulmonary embolism (PE) into risk groups by quantifying the pre-test probability. It is different than Wells score for DVT (deep vein thrombosis). It was originally described by Wells et al. in 1998,^[1] using their experience from creating Wells score for DVT in 1995.^[2] Today, there are multiple (revised or simplified) versions of the rule, which may lead to ambiguity.^[1][3][4]

The purpose of the rule is to select the best method of investigation (e.g. D-dimer testing, CT angiography) for ruling in or ruling out the diagnosis of PE, and to improve the interpretation and accuracy of subsequent testing, based on a Bayesian framework for the probability of the diagnosis.

The rule is more objective than clinician gestalt, but still includes subjective opinion (unlike e.g. Geneva score).

Original algorithm[1]

Originally it was developed in 1998 to improve the low specificity of V/Q scan results (which then had a more important role in the workup of PE than now).

It categorized patients into 3 categories: low / moderate / high probability. It was formulated in the form of an algorithm, not a score.

Subsequent testing choices were V/Q scanning, pulmonary angiography, and serial compression ultrasound.

Revised score [3][4]

The emergence of rapid D-dimer assays in 1995^[5] prompted revision of the rule. The D-dimer assay and the revised Wells score can be combined to identify a population with a pre-test probability of PE of less than 2%.^[6]

This version was published as a score, and according to the final score, patients could be categorized in either 3 groups (low / intermediate / high risk) or 2 groups (PE unlikely/ PE likely).

Subsequent testing choices included D-dimer testing for low risk cases to further understand the pre-test probability; and V/Q scanning, pulmonary angiography, and compression ultrasonography for intermediate / high risk patients and low-risk patients with positive D-dimer results.

Wells score for PE ^[3]

Variable	Points
Clinical signs and symptoms of DVT	3
An alternate diagnosis is less likely than PE	3
Heart rate >100	1.5
Immobilization or surgery in the previous 4 weeks	1.5
Previous DVT / PE	1.5
Hemoptysis	1
Malignancy (treatment currently, in the previous 6 months, or palliative)	1

Risk of PE using 3 categories (data from the derivation group)

Risk group	Points required	Risk of PE
Low risk	0-1	3.6%
Moderate risk	2-6	20.5%
High risk	>6	66.7%

Risk of PE using 2 categories (data from the derivation group)

Risk group	Points required	Risk of PE
Low	0-4	5.1%
High	>4	39.1%