# External validation of risk scores and multivariate models for the diagnosis of community-acquired pneumonia in outpatients

## TL;DR

This study validates existing risk scores for diagnosing community-acquired pneumonia in outpatient settings, finding that the GRACE score performs well with or without CRP data.

## Contribution

The GRACE risk score for CAP diagnosis is externally validated in a US outpatient population, showing robust performance.

## Key findings

- The GRACE risk score with CRP achieved an AUROCC of 0.81, classifying patients into low, moderate, and high CAP risk groups.
- The GRACE score without CRP performed similarly, suggesting clinical exam findings alone can be effective.
- Other risk scores had poor calibration or failed to accurately classify patients into risk categories.

## Abstract

While several risk scores for the diagnosis of community-acquired pneumonia (CAP) have been developed, they require prospective external validation.

To externally validate existing prediction models, risk scores, and heuristics for the diagnosis of CAP in adults.

The Enhancing Antibiotic Stewardship in Primary Care (EAST-PC) study recorded signs, symptoms, demographics, and vitals in 718 adults presenting to primary or urgent care clinics with acute lower respiratory tract infection between 2019 and 2023. C-reactive protein (CRP) was available for 575. The diagnosis of CAP was based on the clinician diagnosis and/or chest radiograph. Literature was searched for previous risk scores. Using the EAST-PC population, the area under the receiver operating characteristic curve (AUROCC), calibration curves, and percentage with CAP in each risk group were calculated for each risk score.

We identified 11 studies describing 4 risk scores, 9 multivariate models, and 5 simple heuristics. The Genomics to Combat Resistance Against Antibiotics in Community-acquired LRTI in Europe (GRACE) risk score using the absence of a runny nose, the presence of breathlessness, crackles, diminished vesicular breathing, heart rate > 100/min, temperature >37.8 °C, and CRP > 30 mg/L was the most accurate (AUROCC 0.81). It classified 280 patients as low (0.7% CAP), 265 as moderate (5.7%) and 30 as high risk (33.3%) for CAP. The GRACE score without CRP performed similarly. Other risk scores had poor calibration or failed to accurately classify patients as low or high risk.

The previously derived GRACE risk scores were successfully externally validated in a contemporary US outpatient population.

Two risk scores using clinical exam findings (with and without CRP) had acceptable accuracy for the diagnosis of community-acquired pneumonia (CAP).Their use classifies about half of patients with lower respiratory tract infections as very low risk for CAPFurther validation studies would be desirable in primary care settings.

Two risk scores using clinical exam findings (with and without CRP) had acceptable accuracy for the diagnosis of community-acquired pneumonia (CAP).

Their use classifies about half of patients with lower respiratory tract infections as very low risk for CAP

Further validation studies would be desirable in primary care settings.