IL6 and COVID-19: However, among COVID-19 patients with disease progression, a significant increase in IL-6 levels from days 4 – 10 (397.65 ng/mL; IQR: 5.55 – 800.86) to days >14 (1248.50 ng/mL; IQR: 798.47 – 1698.52) from illness onset was observed (p < 0.05).