F2 and COVID-19: Second, numerous studies have shown that the disease progression of COVID-19 is not only associated with LDH [2,8-11], lymphocyte [12,13], and hs-CRP [2,10,14-17] but also with other blood-based biomarkers, such as neutrophil counts [16,18,19], albumin [18,20,21], and prothrombin activity [18,22-24].