Lymphopenia is the most frequently described prognostic marker in COVID-19 (Table 1), and it appears to predict morbidity and mortality even at early stages (Fei et al., 2020). Tan et al. proposed a prognostic model based on lymphocyte counts at two time points: patients with less than 20% lymphocytes at days 10–12 from the onset of symptoms and less than 5% at days 17–19 had the worst outcomes in this study (Tan et al., 2020a). Wynants et al. compared predictors of disease severity across seven studies (>1,330 patients), highlighting CRP, neutrophil-to-lymphocyte ratio (N/L), and lactate dehydrogenase (LDH) as the most significant predictive biomarkers (Wynants et al., 2020). Furthermore, a meta-analysis of 30 COVID-19 studies with a total of 53,000 patients also attempted to identify early-stage patients with poor prognosis (Zhao et al., 2020d). The most consistent findings across the different studies were elevated levels of CRP, LDH, and D-dimer, as well as decreased blood platelet and lymphocyte counts (Yan et al., 2020b, Zhou et al., 2020d). Systemic and pulmonary thrombi have been reported with activation of the extrinsic coagulation cascade, involving dysfunctional endothelium and monocytic infiltration (Poor et al., 2020, Varga et al., 2020); thrombocytopenia and elevated D-dimer levels may be indicative of these coagulopathies in COVID-19 patients with important therapeutic implications (Fogarty et al., 2020, Poor et al., 2020).