To analyze the characteristics of clinical and laboratory data of coronavirus disease 2019 (COVID-19) patients with different severity on admission, and to find a laboratory indexes for early warning mild/moderate development into severe/critical type.

Total of 44 patients confirmed with COVID-19 were included in the Department of Infectious Diseases, Zhongnan Hospital of Wuhan University in February 2020, retrospectively. Patients with COVID-19 were divided into mild/moderate group (28 patients) and severe/critical group (16 patients). Blood routine tests [white blood cell (WBC), neutrophil (NEU), lymphocyte (LYM), monocytes (MON), platelet (PLT)], biochemical examinations [alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin (TBil), albumin (ALB), creatinine (CREA)], inflammatory factors tests [C-reactive protein (CRP), interleukin-6 (IL-6)], new coronavirus nucleic acid tests and peripheral blood lymphocyte subsets tests performed within 3 days on admission were collected and analyzed by t test, rank sum test or chi-square test, respectively. The risk factors of severe disease were analyzed by Binary Logistic regression analysis.

Levels of peripheral blood WBC, NEU, MON, PLT, LYM, and absolute count of CD3⁺ T lymphocytes, CD3⁺CD4⁺T lymphocyte, CD3⁺CD8⁺T lymphocytes, CD4⁺/CD8⁺ T, CD19⁺B lymphocytes, CD16⁺CD56⁺NK cells of patients in severe/critical group were all lower than those of mild/moderate group, among which, the absolute count of CD3⁺ T lymphocytes (t = 2.24, P = 0.03), CD3⁺CD4⁺ T lymphocytes (t = 2.148, P = 0.037) and peripheral blood lymphocytes (t = 2.039, P = 0.047) were decreased with significant difference. Serum IL-6 level was 21.06 (11.02, 36.43) pg/ml of patients in severe/critical group and 6.13 (3.14, 12.54) pg/ml in mild/moderate group, with significant difference (Z = 2.952, P = 0.003). Novel coronavirus nucleic acid Ct values ??of respiratory tract specimens and fecal specimens of patients in severe/critical group were (30.03 ± 1.196) and (33.12 ± 1.48), which were significantly lower than those of mild/moderate group: (33.56 ± 0.75) of respiratory tract specimens (t =2.634, P = 0.012) and (35.76 ± 0.98) of fecal specimens (t =1.545, P = 0.130) with significant differences. The length of hospital stay of patients in severe/critical group was (25.06 ± 3.01) days, which was significantly higher than that of mild/moderate group [(11.79 ± 1.06) days], with significant difference (t = 4.986, P < 0.001). Binary Logistic regression analysis found that IL-6 (OR = 1.059, 0.039) and the length of hospital stay (OR = 1.173, 0.005) were both the influencing factors of the severity of patients with COVID-19.

There were significant differences in lymphocyte subsets, serum IL-6 level and viral nucleic acid levels between COVID-19 patients with varying severity, and the length of hospital stay and abnormally increased IL-6 were risk factors for severe disease, and both were of great significance in predicting the severity and clinical classification of COVID-19 patients at early stage.