Comparative Impact of C-Reactive Protein Testing in Hospitalized Patients with Acute Respiratory Tract Infection: A Retrospective Cohort Study

Introduction Evidence-based data on the usefulness of C-reactive protein (CRP) monitoring in patient outcomes are lacking. CRP testing in patients with acute respiratory tract infections (ARTIs) showed wide variability between internal medicine wards in our hospital network. In this study we aimed to investigate whether repetitive CRP tests might influence the switch of antibiotic therapy from intravenous (IV) to oral (PO) route and whether CRP measurements affect the combined outcome of readmission and in-hospital mortality. Methods This was a retrospective cohort study conducted in two internal medicine wards selected in a network of five teaching hospitals on the basis of their CRP prescription frequency. Clinical and laboratory data of 296 patients with ARTIs and admitted from 1 January to 31 December 2016 were analyzed. Results The mean +/- SD of CRP tests/patient and the in-hospital length of antibiotic therapy (days) in the low-CRP (L-CRP) vs the high-CRP (H-CRP) wards were 1.14 +/- 0.62 vs 3.43 +/- 1.54 (p < 0.001) and 7.1 +/- 2.6 vs 7.5 +/- 3.2 (p = 0.298), respectively. The probability of antibiotic switching was higher in the L-CRP ward (HR 2.90, 95% CI 1.69-4.95, p < 0.001) correlating with the lower number of CRP determinations (HR 1.20, 95% CI 1.01-1.41, p = 0.034). In-hospital readmissions and mortality rates did not significantly differ between the two wards (L-CRP 17.1% vs H-CRP 10.0%, p = 0.133). The number of CRP determinations affected the combined outcome (OR 1.38, 95% CI 1.01-1.90, p = 0.043). Conclusions Repetitive CRP testing in ARTIs offers no added value to either antibiotic switch or patient outcomes in hospitalized patients in internal medicine wards.