Usefullness of CPR and PCT in the etiological diagnosis of community-acquired pneumonia

Abstract

Background: Biomarkers - C-reactive protein (CRP) and procalcitonin (PCT)- in community-acquired pneumonia (CAP) could be useful to distinguish bacterial or viral etiology.

Objective: To analyse initial levels of CRP and PCT in hospitalised CAP according to etiological diagnosis.

Material and method: Prospective observational study in 685 patients. The etiology of CAP was classified as bacterial, viral and atypical (Mycoplasma, Coxiella and Chlamydophila). We have calculated the cut-off points of PCT and CRP to differentiate bacterial or viral etiology and its diagnostic value through sensitivity (S), specificity (E), positive predictive value (PPV) and negative predictive value (NPV).

Results: An etiological diagnosis was reached in 295 (43%) patients: 203 (29.6%) bacterial - 118 S pneumoniae (51.1%) and 24 Legionella (11.8%)-, 12 (1.8%) virus and 24 (3.5%) atypical. The comparison between Legionella vs S pneumoniae with a cut off CRP≥22 and S:70%. E:59%. PPV:27%. NPV:90%; Atypical vs Bacteria with a threshold of PCT<0.5 and S:81%. E:68%. PPV:22%. NPV:97%; Virus vs Bacteria with a cut off PCT<0.5 and S:89%. E:68%. PPV:12%. NPV:99%.

Conclusion: A threshold of PCT>0.5 rules out viral etiology with a very high negative predictive value. Legionella is associated with initial higher CRP. CRP and PCT do not allow to differentiate between viral or atypical etiology.