*4.5. CRP as Marker of Disease Activity in COVID-19*

In our cases the patients with the highest CRP values within 3 days of disease onset were those that had the most severe COVID-19 disease evolution. All patients with a CRP level ≥199 mg/L were treated in the ICU and died. CRP is a marker of COVID-19 disease activity. It is a plasma protein that is produced in the liver. Various mediators of inflammation, such as Interleukin (IL-)6, can induce CPR production. Elevation of CRP levels in COVID-19 are associated with the severity of COVID-19. Compared to the erythrocyte sedimentation rate (ESR), CRP levels were significantly greater during early periods of severe COVID-19 cases and were shown to be a more sensitive biomarker in reflecting disease development [26,27]. In a retrospective study, the majority of patients with severe COVID-19 showed significantly higher CRP levels as in the non-severe COVID-19 patients (57.9 mg/L vs. 33.2 mg/L, *p* < 0.001) [28]. Another retrospective study showed

that CRP can effectively assess disease severity and predict outcomes in patients with COVID-19, with an increased risk of progression to a higher severity stage in patients with CRP levels >41.8 mg/L [29–31]. CRP values were found to be a more reliable indicator for earlier identification of case severity than CT scans alone [26].
