Ferritin is an iron storage protein that represents the primary source of reserve iron in each cell. Measurement of serum ferritin concentration gives a quantitative determination of the mobilizable storage iron. However, increased serum ferritin concentrations can also be suggestive of conditions not related to iron storage, such as severe inflammation. Therefore, the IFCC recommends monitoring of serum ferritin levels for COVID-19 management. [1,2]
A retrospective, multicenter cohort study of 191 COVID-19 patients showed that among other parameters, elevated serum ferritin levels was associated with death.  Another study of 150 COVID-19 cases confirmed elevated inflammatory indicators, such as ferritin, as a predictor of fatality. In non-survivors mean serum ferritin levels was 1297.6 ng/mL, while it was only 614.0 ng/mL in survivors (p<0.001). The study concluded that the mortality was likely due to virally driven hyperinflammation. 
Mehta et al. advises to screen all patients with severe COVID-19 for hyperinflammation, by monitoring laboratory trends, including serum ferritin concentrations.