Inflammatory Markers Are Not Useful for Identifying Patients With SARS-CoV-2 Infection

Korley, Frederick K.; Nelson, Jacob R.; Holmes, Adam R.; Hirschl, Jacob R.; Sidney, J.; Chopra, Perkins Zoey; Medlin, Richard P.; Fung, Christopher

Background: Due to the limited availability of rapid testing for SARS-CoV-2 infection, these tests are often reserved for those requiring urgent procedures or hospital admission and are often not available to emergency department (ED) patients. Complete blood count (CBC), C-reactive protein (CRP) and Ferritin levels can be easily obtained in the ED. Lymphopenia and high C-reactive protein and Ferritin levels are associated with poor outcome in COVID-19 illness. However, it is not known whether these biomarkers are useful for identifying persons with SARS-CoV-2 infection. Methods: We performed a cross-sectional study of patients 18 years or older who were evaluated at an academic ED for suspected SARS-CoV-2 infection from March to May 2020. CBC, CRP and Ferritin levels were ordered at clinician’s discretion in patients who were suspected to have SARS-CoV-2 infection. SARS-CoV-2 infection was diagnosed using a number of PCR-based tests including the Cepheid Xpert Xpress and the Diasorin Simplexa. The discriminative values of the candidate biomarkers were estimated using the area under the receiver operating characteristic curve (AUC). Results: We studied a total of 1082 patients who had a median age of 59.5 (IQR: 46.0 – 71.0) years. A total of 431 (39.8%) of the subjects had PCR confirmed SARS-CoV-2 infection. The median absolute lymphocyte count was 0.9 (IQR: 0.7 – 1.3) and 1.0 (0.7 – 1.6) in those with and those without SARS-CoV-2 infection respectively (p=0.0004). The median CRP level in mg/L was 8.9 (IQR: 4.6 – 17.3) and 6.1 (IQR: 1.6 – 14.0) in those with and those without SARS-CoV-2 infection respectively (p=0.0001). The median ferritin level in ng/mL was 782 (IQR: 299 – 1479) and 312 (IQR: 106 – 1015) in those with and those without SARS-CoV-2 infection respectively (p=0.0001). Lymphocyte count, CRP and Ferritin levels distinguished between those with and those without SARS-CoV-2 infection with AUCs of 0.56 (IQR: 0.53 – 0.60), 0.61 (IQR: 0.58 – 0.64) and 0.66 (IQR: 0.62 – 0.68). Conclusion: Although patients with SARS-CoV-2 infection have lymphopenia and elevated CRP and ferritin levels, the levels of these biomarkers are not useful for identifying persons under investigation who have SARS-CoV-2 infection.