Because total leukocyte count, neutrophils, lymphocytes, CRP, NLR, PLR and CLR were markedly altered in patients with severe disease, we then further evaluated the possibility of using these markers in guiding types of oxygen therapy in COVID-19 patients by analyzing the median values among patients receiving oxygen mask bag, low flow oxygen cannula, high-flow nasal cannula and invasive mechanical ventilator. The gene discussed is CRP; the disease is COVID-19.