Background: Studies have tried to determine the diagnostic value of serum inflammatory biomarkers in patients with community-acquired pneumonia (CAP) to help guide clinical decision making. This study aimed to determine the relationship between white blood cell (WBC), neutrophil-to-lymphocyte ratio (NLR), procalcitonin (PCT), and severe CAP. Methodology: This study reviewed records of patients aged 18 years and above diagnosed with CAP from January 2022 to January 2024 at Perpetual Help Medical Center—Las Piñas. Data collected were demographics, WBC and neutrophil and lymphocyte counts, procalcitonin, and CURB-65 scores. ROC curve analysis was done to determine the best cut-off for WBC, NLR, and procalcitonin in diagnosing severe CAP (CURB-65 score 3-5). Pearson correlation test was used to determine pairwise correlations between WBC, NLR, and procalcitonin. Results: A total of 120 patients were included. The mean WBC count and mean NLR were higher among patients with elevated PCT than those with normal PCT (15.2 ± 5.8 vs 10.7 ± 3.7; p <0.001 and 18.6 ± 17.9 vs 8.6 ± 7.9; p = 0.005, respectively). The prevalence of severe pneumonia was higher in patients with elevated PCT than those with normal PCT (65.8% vs 12.8%; p <0.001). Procalcitonin level at a threshold of 0.5 ng/mL showed the highest sensitivity (90%, 95% confidence interval [CI] 0.77 to 0.97) and best test performance (area under the ROC 0.79, 95% CI 0.72 to 0.86) in diagnosing severe pneumonia. The mean NLR was weakly correlated with WBC (r = 0.300; p = 0.002). The mean PCT was moderately correlated with WBC (r = 0.637, p = 0.04) and NLR (r = 0.750, p = 0.03). Conclusion: Procalcitonin shows acceptable performance in diagnosing severe pneumonia. This study also suggests a significant correlation between WBC, NLR, and PCT. Multicenter studies are recommended to better generalize the results to the larger population.
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