Role of Serum Biomarkers(Procalcitonin and CRP) in differentiating Bacterial VS Viral Lower Respiratory Tract Infections (LRTIS)

Abstract

Objective: To compare the diagnostic accuracy of serum procalcitonin and C-reactive protein, alone and in combination, for differentiating bacterial from viral lower respiratory tract infections.

Study Design: Prospective observational cohort study
Place and Duration of Study: This study was conducted at the Pulmonology Deptt, Liaquat University of Medical & Health Sciences (LUMHS), Jamshoro between March 2024 to February 2025.

Methods: Two hundred patients with LRTIs were recruited (120 bacterial, 80 viral). The admission levels of serum PCT and CRP were determined using chemiluminescent immunoassay and ELISA, respectively. The etiology of bacteria was determined through the culture and sensitivity tests, and the etiology of viral infections was determined by PCR. Receiving operating characteristic (ROC) curves were used to evaluate diagnostic accuracy.

Results: The mean PCT levels were statistically much higher in bacterial LRTIs (5.2 ± 3.1 ng/mL) than viral LRTIs (0.4 ± 0.3 ng/mL). Similarly, mean CRP levels were elevated in bacterial (92.1 ± 34.5 mg/L) versus viral infections (45.2 ± 29.3 mg/L; p < 0.001). The PCT area under the curve (AUC) was 0.88 (sensitivity: 85%, specificity: 90% at cut-off >0.5 ng/mL), and compared to 0.76 of CRP (sensitivity: 70%, specificity: 65% at cut-off >50 mg/L). The combination of both biomarkers greatly enhanced diagnostic performance (sensitivity: 92%, specificity: 93%; PPV: 97%, NPV: 91; p < 0.001).

Conclusion: Procalcitonin has better diagnostic accuracy than C-reactive protein to differentiate between bacterial and viral LRTIs. Both biomarkers combined improve diagnostic performance and clinical decision making and may lead to fewer unnecessary antibiotic prescriptions. It is suggested that biomarker thresholds need to be validated locally.