Comparison between C reactive protein and procalcitonin in patients with respiratory tract infection and autoimmune disease

Background and aims: C reactive protein (CRP) and procalcitonin (PCT) are markers of inflammation. The aim of this study was to compare CRP and PCT in patients with infectious disease and in those with autoinflammatory disorder. Methods: Hospitalized children with respiratory tract infection (RTI) (n=61) and children with autoimmune disease (AD) (n=47) were prospectively enrolled. At admission, blood samples were taken to determine the level of CRP (automated enzyme-linked immunoassay, negative value < 0.5 mg/dL) and PCT (immunoluminometric assay, negative value < 0.25 ng/mL). Clinical data were collected during hospitalization. Results: Among children with RTI, PCT < 0.5 ng/mL was identified in 30/36 (83.3%) children with confirmed viral etiology, whereas CRP < 1 mg/dL was observed only in 4/36 children (11.1%; p< 0.0001). Conversely, PCT >0.5 ng/mL was identified in 23/25 (92.0%) children with confirmed bacterial etiology, whereas CRP >1 mg/dL was detected in 24/25 children (96%). Among children with AD, in the active and in the stable phase of the disease PCT was always < 0.5 ng/mL, whereas PCR < 1 mg/dL was observed only in 11/32 children in active phase (34.4%; p< 0.0001) and in 2/15 of those stable (13.3%). Conclusions: PCT seems a sensible and specific marker that permits to distinguish bacterial from viral etiology in patients with RTI. In contrast with CRP, the value of PCT does not seem to be affected by the inflammatory status. These findings suggest to use PCT for deciding when to start antimicrobial therapy in children with RTI or AD.