CRP and COVID-19: Although procalcitonin (PCT) was a biomarker that was shown to differentiate viral and bacterial pneumonia in prepandemic studies,42,43in COVID-19, it is frequently a marker of severe disease rather than bacterial coinfection.44 A meta-analysis of 4,911 patients from 29 studies found that WBC count >10×109/L, PCT >0.5 ng/mL, and CRP >10 mg/L were risk factors for COVID-19 disease progression.45 Bacterial infections can also produce some of the same findings.