PESI vs Wells score: probability before diagnosis, prognosis after

What is the difference between PESI and the Wells score?

The difference between PESI and the Wells score is the question each one answers. The Wells score for pulmonary embolism, published by Wells and colleagues in Thrombosis and Haemostasis in 2000, is a diagnostic rule: it estimates the clinical probability that a patient with suspected PE actually has it, so that testing can be chosen. The Pulmonary Embolism Severity Index, published by Aujesky and colleagues in the American Journal of Respiratory and Critical Care Medicine in 2005, is a prognostic rule: it estimates the risk of death from any cause within 30 days in a patient whose PE has already been diagnosed. The simplified PESI (sPESI) of Jiménez and colleagues, published in 2010, answers the same prognostic question with six items. Wells is scored before imaging and PESI after it, so the two are steps in sequence rather than rival scores. Using Wells to judge severity, or PESI to decide whether PE is present, applies each score outside the population it was built on.

The Wells score: how likely is pulmonary embolism?

The Wells score estimates how likely pulmonary embolism is in a patient in whom it is suspected. Wells and colleagues ran a logistic regression on 40 clinical variables in a random 80% of a prospective cohort and kept seven: clinical symptoms of deep vein thrombosis (3 points), no alternative diagnosis (3), heart rate over 100 (1.5), immobilization or surgery in the previous four weeks (1.5), previous DVT or PE (1.5), hemoptysis (1) and malignancy (1). The total runs from 0 to 12.5. In the three-level reading, under 2 is low, 2 to 6 is moderate and over 6 is high probability. In the two-level reading, 4 or less is PE unlikely and over 4 is PE likely. In the derivation set, 7.8% of patients scoring 4 or less had PE, and only 2.2% when the SimpliRED D-dimer was also negative. None of the seven items measures how ill the patient is, and a high Wells score says nothing about the outcome once PE is found.

Score it with the Wells score for PE calculator.

PESI and sPESI: how sick is the patient with confirmed PE?

PESI and sPESI estimate how likely a patient with confirmed pulmonary embolism is to die within 30 days. Aujesky's PESI adds the age in years to points for male sex (10), cancer (30), heart failure (10), chronic lung disease (10), pulse of 110 or more (20), systolic blood pressure below 100 mmHg (30), respiratory rate of 30 or more (20), temperature below 36 °C (20), altered mental status (60) and arterial oxygen saturation below 90% (20). Totals of 65 or less are class I, 66 to 85 class II, 86 to 105 class III, 106 to 125 class IV and over 125 class V, with 30-day mortality from 0–1.6% in class I to 10.0–24.5% in class V across the three samples. The sPESI gives 1 point each for age over 80, cancer, chronic cardiopulmonary disease, pulse of 110 or more, systolic pressure below 100 and saturation below 90%. A score of 0 carried a 30-day mortality of 1.0% at derivation and 1.1% in RIETE validation.

The PESI score calculator scores both from one set of answers and shows the mortality figures for each class.

Where the PERC rule and the ESC risk classes fit

The PERC rule and the ESC risk classes sit at either end of the Wells-to-PESI sequence. The pulmonary embolism rule-out criteria of Kline and colleagues (2004) come first, only in patients judged low risk: age under 50, pulse under 100, SaO2 of 95% or more, no unilateral leg swelling, no hemoptysis, no recent surgery or trauma, no prior PE or DVT and no hormone use. In Kline's 2008 study of 8,138 emergency patients, low suspicion plus a negative PERC carried a 1.0% rate of venous thromboembolism or death within 45 days. At the other end, the 2019 ESC guideline on acute PE uses PESI and sPESI inside a wider classification of the risk of early death. It defines high-risk PE by haemodynamic instability, and states that a PESI of class I–II or an sPESI of 0 is a reliable predictor of low-risk PE. Patients with right ventricular dysfunction or raised cardiac biomarkers despite such a score are classed as intermediate risk.

For the rule-out step, use the PERC rule calculator; for how PERC compares with Wells, read PERC vs Wells.

Worked examples: the same patients on both scores

Two patients show why a high Wells score does not predict a high PESI score, even though both rules count cancer and heart rate. A 58-year-old woman with active cancer arrives with a heart rate of 115 and no likelier alternative diagnosis. Her Wells score is 3 for no alternative diagnosis, 1.5 for heart rate over 100 and 1 for malignancy, a total of 5.5: moderate probability and PE likely. Imaging confirms PE. With every other PESI finding normal, her PESI is 58 plus 30 for cancer plus 20 for the pulse: 108, class IV, where 30-day mortality ranged from 4.0% to 11.4%. Her sPESI is 2, high risk. A 45-year-old man three weeks after knee surgery has a heart rate of 104 and no alternative diagnosis. His Wells score is 6, also PE likely. Once PE is confirmed, his PESI is 45 plus 10 for male sex: 55, class I. His pulse is under 110, so his sPESI is 0, low risk.

The heart-rate cut-offs differ: Wells counts a rate over 100, while PESI and sPESI count 110 or more. Enter both patients in the PESI score calculator to see the same classes.