Warning indicators of COVID-19 severity: a retrospective observational study integrating modern biomarkers and traditional tongue features - Jing, Zhang; Yuntao, Liu; Danwen, Zheng; Gangfu, Ye; Qiumin, Chen; Jianshan, Huang; Jiamei, Wang; Zengming, Ma; Zhongde, Zhang (Frontiers in Medicine, 2025)