Among patients in the emergency department, dyspnea is a common complaint and can pose a diagnostic challenge. Biomarkers are used increasingly to improve diagnostic accuracy and aid with prognostication in dyspneic patients. The purpose of this study was to examine the clinical utility of serum procalcitonin (PCT) for the diagnosis of pneumonia in patients presenting to the emergency department with dyspnea. A secondary objective was to evaluate the prognostic value of PCT for death to 1 year.

This study pooled the patient populations of 2 prospective cohorts that previously enrolled patients presenting to 2 urban emergency departments with dyspnea. A total of 453 patients had serum samples available for biomarker analysis. Clinician certainty for the diagnosis of acutely decompensated heart failure was reviewed. Discrimination, calibration, and net reclassification improvement for the diagnosis of pneumonia as well as fatal outcomes were considered. The main outcome was accuracy of PCT for diagnostic categorization of pneumonia. The prognostic value of PCT for survival to 1 year was a secondary outcome.

Pneumonia alone was diagnosed in 30 patients (6.6%), heart failure without pneumonia in 212 patients (47%), and both diagnoses in 30 patients (6.6%). Procalcitonin concentrations were higher in subjects with pneumonia (0.38 vs 0.06 ng/mL; P < .001). Area under the receiver operating characteristic curve for the diagnosis of pneumonia based on PCT was 0.84 (95% confidence interval [CI], 0.77-0.91; P < .001). Across all levels of clinician-based estimates of heart failure, PCT was sensitive and specific; notably, in patients judged with diagnostic uncertainty (n = 70), a PCT value of 0.10 ng/mL had the optimal balance of sensitivity and specificity (80% and 77%, respectively) for pneumonia. Adding PCT results to variables predictive of pneumonia resulted in a net reclassification improvement of 0.54 (95% CI, 0.24-0.83; P < .001) for both up- and down-reclassifying events. In adjusted analyses, elevated PCT was a predictor of 1-year mortality (hazard ratio 1.8; 95% CI, 1.4-2.3; P < .001) and was additive when elevated in conjunction with natriuretic peptides for this application.

In emergency department patients with acute dyspnea, PCT is an accurate diagnostic marker for pneumonia and adds independent prognostic information for 1-year mortality.