A total of 1258 confirmed COVID-19 patients were admitted into the two hospitals. Of these, 653 patients were ruled out for one of the following reasons: (1) no definitive 28-day outcome since they were transferred to another hospital; (2) missing key clinical information (e.g. demographic or clinical data); (3) no FBG data available at admission (for one of the following reasons: [a] patients had a blood glucose measurement taken before admission; [b] patients were tested for blood glucose 24 h after admission; [c] patients received a random blood glucose test but were not tested for FBG; [d] patients did not receive a blood glucose test since this was not routinely conducted for every COVID-19 patient); (4) having previously diagnosed diabetes. The flow diagram of patient selection is detailed in Fig. 1.
Fig. 1 Flow diagram of patient selection. aReasons for no FBG measurement at admission: 13 patients had a blood glucose measurement taken before admission; 25 patients were tested for blood glucose 24 h after admission; 84 patients received a random blood glucose test but were not tested for FBG; and 81 patients did not receive a blood glucose test since this was not routinely conducted for every COVID-19 patient