Diagnostic utility of a Ferritin-to-Procalcitonin Ratio to differentiate patients with COVID-19 from those with Bacterial Pneumonia: A multicenter study

Gharamti, Amal A; Mei, Fei; Jankousky, Katherine C; Huang, Jin; Hyson, Peter; Chastain, Daniel B; Fan, Jiawei; Osae, Sharmon; Zhang, Wayne W; Montoya, José G; Erlandson, Kristine M; Scherger, Sias J; Franco-Paredes, Carlos; Henao-Martínez, Andrés F; Shapiro, Leland

BACKGROUND: There is an urgent need for accurate, rapid, inexpensive biomarkers that can differentiate COVID-19 from bacterial pneumonia. We assess the role of the ferritin-to-procalcitonin (F/P) ratio to classify pneumonia cases into those due to COVID-19 or due to bacterial pathogens. METHODS: This multicenter case-control study compared patients with either COVID-19 and bacterial pneumonia, admitted between March 1 and May 31, 2020. Patients with COVID-19 and bacterial pneumonia co-infection were excluded. The F/P in patients with COVID-19 or with bacterial pneumonia were compared. Receiver operating characteristic analysis determined the sensitivity and specificity of various cut-off F/P values for COVID-19 versus bacterial pneumonia. RESULTS: A total of 242 COVID-19 pneumonia cases and 34 bacterial pneumonia controls were included. Patients with COVID-19 pneumonia had a lower mean age (57.11 vs 64.4 years, p=0.02) and a higher BMI (30.74 vs 27.15 kg/m 2, p=0.02) compared to patients with bacterial pneumonia. Cases and controls had a similar proportion of women (47% vs 53%, p=0.5) and COVID-19 patients had a higher prevalence of diabetes mellitus (32.6% vs 12%, p=0.01). The median F/P was significantly higher in patients with COVID-19 (4037.5) compared to the F/P in bacterial pneumonia (802, p<0.001). An F/P ≥ 877 used to diagnose COVID-19 resulted in a sensitivity of 85% and a specificity of 56%, with a positive predictive value of 93.2%, and a likelihood ratio of 1.92. In multivariable analyses, an F/P ≥ 877 was associated with greater odds of identifying a COVID-19 case (OR: 11.27, CI: 4-31.2, p<0.001). CONCLUSION: An F/P ≥ 877 increases the likelihood of COVID-19 pneumonia compared to bacterial pneumonia.