GFAP and COVID-19: However, the overall pooled GFAP level showed a significant difference between COVID-19 patients with severe and mild disease (SMD = 0.85; 95% CI: 0.46, 1.24; Z = 4.23; p ≤ 0.001) with heterogeneity (I2: 54%) (second panel from the top, Figure 3), indicating that the concentration of biomarkers in mild COVID-19 was lower than the severe cases.