Study of serum Procalcitonin and C-reactive protein in differentiating bacterial from viral lower respiratory tract infections

Abstract

Background: Differentiating bacterial from viral lower respiratory tract infections (LRTIs) remains a clinical challenge, often leading to inappropriate antibiotic use. Biomarkers such as serum procalcitonin (PCT) and C-reactive protein (CRP) may aid in early distinction.

Objective: To evaluate the diagnostic utility of serum procalcitonin and CRP in differentiating bacterial from viral LRTIs.

Methods: This prospective cross-sectional study was conducted April 2025 to March 2026 including 115 patients presenting with LRTI. Patients were classified into bacterial and viral groups based on clinical, radiological, and microbiological findings. Serum PCT and CRP levels were measured and compared.

Results: Mean PCT levels were significantly higher in bacterial infections (2.8 ± 1.2 ng/mL) compared to viral infections (0.6 ± 0.3 ng/mL; p < 0.001). Similarly, CRP levels were elevated in bacterial cases (65 ± 20 mg/L) versus viral cases (18 ± 10 mg/L; p < 0.001). PCT demonstrated higher specificity compared to CRP.

Conclusion: Both PCT and CRP are useful biomarkers, but PCT shows superior accuracy in distinguishing bacterial from viral LRTIs, aiding in rational antibiotic use.

Keywords: lower respiratory tract infections (LRTIs), procalcitonin (PCT), C-reactive protein (CRP), bacteria, antibiotic