Objective::To investigate and analyze changes of T lymphocyte and other lymphocyte subsets in the peripheral blood of patients with coronavirus disease 2019 (COVID-19), with the goal of improving clinical understanding and the value of research applications.Methods::General data of 66 confirmed COVID-19 patients admitted to the Fifth Medical Center of Beijing PLA General Hospital from January 2 to March 23, 2020 were collected in this retrospective case-control observational study, and they were divided into mild (n n=26), mid-grade (n n=19), and severe/critical disease groups (n n=21) according to disease severity. Neutrophils, lymphocytes, neutrophil/lymphocyte ratios, CD4 absolute counts, CD8 absolute counts, and CD4/CD8 expression ratios of peripheral whole blood among the three patient groups were compared. The study protocol was approved by the Ethics Committee of the Fifth Medical Center, General Hospital of Chinese PLA (approval No. 2020-69-D) on May 5, 2020.n Results::Among the 66 COVID-19 patients examined, 38 were male and 28 were female, with an average age of 53 ± 17 years. Among patients, 26 cases were mild, 19 cases were mid-grade, and 21 cases were severe/critical. Neutrophils, neutrophil/lymphocyte ratios, and CD4n +/CD8n + ratios of the severe/critical group were significantly higher compared with mild and mid-grade groups (n P 0.05). Lymphocytes, CD4 absolute counts, and CD8 n + absolute counts of the severe/critical group were significantly lower compared with mild and mid-grade groups (n P 0.05).n Conclusion::Counts of lymphocytes and T lymphocytes in severe/critically ill patients were decreased, which is of great significance for the identification of severe and critical COVID-19 patients.“,”Objective::To investigate and analyze changes of T lymphocyte and other lymphocyte subsets in the peripheral blood of patients with coronavirus disease 2019 (COVID-19), with the goal of improving clinical understanding and the value of research applications.Methods::General data of 66 confirmed COVID-19 patients admitted to the Fifth Medical Center of Beijing PLA General Hospital from January 2 to March 23, 2020 were collected in this retrospective case-control observational study, and they were divided into mild (n n=26), mid-grade (n n=19), and severe/critical disease groups (n n=21) according to disease severity. Neutrophils, lymphocytes, neutrophil/lymphocyte ratios, CD4 absolute counts, CD8 absolute counts, and CD4/CD8 expression ratios of peripheral whole blood among the three patient groups were compared. The study protocol was approved by the Ethics Committee of the Fifth Medical Center, General Hospital of Chinese PLA (approval No. 2020-69-D) on May 5, 2020.n Results::Among the 66 COVID-19 patients examined, 38 were male and 28 were female, with an average age of 53 ± 17 years. Among patients, 26 cases were mild, 19 cases were mid-grade, and 21 cases were severe/critical. Neutrophils, neutrophil/lymphocyte ratios, and CD4n +/CD8n + ratios of the severe/critical group were significantly higher compared with mild and mid-grade groups (n P 0.05). Lymphocytes, CD4 absolute counts, and CD8 n + absolute counts of the severe/critical group were significantly lower compared with mild and mid-grade groups (n P 0.05).n Conclusion::Counts of lymphocytes and T lymphocytes in severe/critically ill patients were decreased, which is of great significance for the identification of severe and critical COVID-19 patients.