Developing the Pneumonia-Optimized Ratio for Community-acquired pneumonia: An easy, inexpensive and accurate prognostic biomarker

Introduction Community-acquired pneumonia (CAP) is still a major public health problem. Prognostic scores at admission in tertiary services may improve early identification of severity and better allocation of resources, ultimately improving survival. Herein, we aimed at evaluating prognostic biomarkers of CAP and a Pneumonia-Optimized Ratio was created to improve prognostic performance. Methods In this retrospective study, all patients with suspected Community-acquired pneumonia aged 18 or older admitted to a public hospital from January 2019 to February 2020 were included in this study. Blood testing and clinical information at admission were collected, and the primary outcome was overall survival. CURB-65 scores and prognostic biomarkers were measured, namely Neutrophil-to-Lymphocyte Cell Ratio (NLCR), Platelet to Lymphocyte ratio (PLR), Monocyte to Lymphocyte Ratio (MLR). A Pneumonia-Optimized Ratio (POR) score was created by selecting the biomarker with larger accuracy (NLCR) and multiplying it by the patients’ CURB-65 score. Multivariate regression model was performed and ROC curves were created for each biomarker. Results Our sample consisted of 646 individuals (median 66 years [IQR, 18–103], 53.9% females) with complete blood testing at the time of admission. Patients scored 0–1 (323, 50%), 2 (187, 28.9%), or 3 or above (122, 18.9%) in the CURB-65, and 65 (10%) presented the primary outcome of death. POR exhibited the highest Area Under Curve (AUC) in the ROC analysis (AUC = 0.753), when compared with NLCR (AUC = 0.706), PLR (AUC = 0.630) and MLR (AUC = 0.627). POR and NLCR presented increased crude mortality rate in the fourth quartile in comparison with the first quartile, and the fourth quartile of NLCR had more days of hospitalization than the first quartile (11.06±15.96 vs. 7.02±8.39, p = 0.012). Conclusion The Pneumonia-Optimized Ratio in patients with CAP showed good prognostic performance of mortality at the admission of a tertiary service. The NLCR may also be used as an estimation of days of hospitalization. Prognostic biomarkers may provide important guidance to resource allocation in resource-limited settings.