Results

Patient characteristics
Up to 10 February 2020, 1258 patients were admitted to Wuhan Union West Hospital or Wuhan Red Cross Hospital for confirmed COVID-19. After excluding 157 patients who were re-directed to other hospitals, 182 patients missing key clinical information, 203 patients without FBG at admission and 111 patients with previous history of diabetes, a total of 605 patients without a previous diagnosis of diabetes (448 from Wuhan Union West Hospital and 157 from Wuhan Red Cross Hospital) were included in the analysis (Fig. 1).
Baseline data of continuous and categorical variables among the groups of survivors and non-survivors are shown in Table 1. The median age of participants was 59.0 years (IQR 47.0, 68.0), and 322 (53.2%) were men. Two hundred and eight patients (34.4%) had one or more past diseases, of which hypertension was the most common comorbidity. At admission, the most common symptoms were fever, followed by cough and fatigue. Three hundred and thirty four patients (55.2%) had a CRB-65 score of 0; 261 (43.1%) had a CRB-65 score of 1–2; 10 (1.7%) had a CRB-65 score of 3–4. The patients were categorised in terms of their glucose levels into three groups: patients with FBG <6.1 mmol/l (n = 329, 54.4%), patients with FBG 6.1–6.9 mmol/l (n = 100, 16.5%) and patients with FBG ≥7.0 mmol/l (n = 176, 29.1%). One hundred and fourteen patients (18.8%) died within 28 days during hospitalisation. Among 605 patients, 237 (39.2%) developed one or more in-hospital complications (Table 1).

Comparison between non-survivors and survivors
Compared with survivors, more non-survivors were found among older people (median age 66.0 years vs 56.0 years, p < 0.0001), male (68.4% vs 49.7%, p = 0.0003), patients with a past medical history (48.3% vs 31.2%, p = 0.0005). In terms of past medical history, cerebrovascular disease (6.1% vs 1.8%, p = 0.0098) was significantly higher in non-survivors than in survivors. In non-survivors, the percentages were higher in patients having CRB-65 score of 3–4 and FBG ≥7.0 mmol/l at admission (Table 1).

Factors associated with in-hospital 28-day mortality
The univariable Cox regression analysis showed that age, male sex, chronic kidney disease, cerebrovascular disease, CRB-65 score and FBG were associated with in-hospital 28-day mortality. The multivariable Cox regression analysis further suggested that age (HR 1.02 [95% CI 1.00, 1.04]), male sex (HR 1.75 [95% CI 1.17, 2.60]), CRB-65 score 1–2 (HR 2.68 [95% CI 1.56, 4.59]), CRB-65 score 3–4 (HR 5.25 [95% CI 2.05, 13.43]) and FBG ≥7.0 mmol/l (HR 2.30 [95% CI 1.49, 3.55]) were independent predictors for mortality (Table 2).
Table 2 Univariable and multivariable analyses of various indicators for death within 28 days in all participants
Univariable analysis HR (95% CI) p value Multivariable analysis HR (95% CI) p value
Hospital
 Wuhan Red Cross Hospital 1 (ref)
 Wuhan Union West Hospital 0.85 (0.57, 1.28) 0.4347
Age, years 1.05 (1.03, 1.06) <0.0001 1.02 (1.00, 1.04) 0.0252
Sex Female 1 (ref) 1 (ref)
Male 2.03 (1.37, 3.01) 0.0004 1.75 (1.17, 2.60) 0.0060
Onset symptoms
 Fever No 1 (ref)
Yes 0.84 (0.48, 1.44) 0.5191
 Cough No 1 (ref)
Yes 0.71 (0.47, 1.08) 0.1125
 Expectoration No 1 (ref)
Yes 1.06 (0.71, 1.58) 0.7788
 Muscular soreness No 1 (ref)
Yes 0.92 (0.57, 1.47) 0.7256
 Fatigue No 1 (ref)
Yes 1.07 (0.72, 1.60) 0.7386
 Diarrhoea No 1 (ref)
Yes 0.83 (0.48, 1.44) 0.5124
Past history of disease
 Hypertension Without 1 (ref)
With 1.27 (0.85, 1.89) 0.2493
 Chronic lung disease Without 1 (ref)
With 1.12 (0.41, 3.03) 0.8285
 Chronic heart disease Without 1 (ref)
With 1.34 (0.75, 2.39) 0.3151
 Chronic liver disease Without 1 (ref)
With 0.95 (0.30, 2.99) 0.9296
 Chronic kidney disease Without 1 (ref)
With 2.28 (1.00, 5.19) 0.0496
 Cerebrovascular disease Without 1 (ref)
With 2.82 (1.31, 6.05) 0.0080
 Carcinoma Without 1 (ref)
With 1.81 (0.92, 3.58) 0.0876
CRB-65 score 0 1 (ref) 1 (ref)
1–2 4.35 (2.81, 6.72) <0.0001 2.68 (1.56–4.59) 0.0003
3–4 13.80 (5.99, 31.80) <0.0001 5.25 (2.05–13.43) 0.0005
Admission FBG, mmol/l <6.1 1 (ref) 1 (ref)
6.1–6.9 2.06 (1.20, 3.54) 0.0087 1.71 (0.99, 2.94) 0.0524
≥7.0 3.54 (2.33, 5.38) <0.0001 2.30 (1.49, 3.55) 0.0002
The cumulative death rate within 28 days in all COVID-19 participants stratified in terms of FBG and CRB-65 score at admission overall is shown in Fig. 2a (ptrend < 0.0001) and Fig. 2b (ptrend = 0.0020). Compared with patients with FBG <6.1 mmol/l, mortality within 28 days was higher in those with FBG of 6.1–6.9 mmol/l (crude HR 2.06 [95% CI 1.20, 3.54]) and ≥7.0 mmol/l (crude HR 3.54 [95% CI 2.33, 5.38]), respectively (Table 2). Compared with patients with FBG of 6.1–6.9 mmol/l, mortality within 28 days was higher in those with FBG ≥7.0 mmol/l (crude HR 1.72 [95% CI 1.05, 2.84]). Meanwhile, compared with patients with CRB-65 score of 0, mortality within 28 days was higher in those with CRB-65 of 1–2 (crude HR 4.35 [95% CI 2.81, 6.72]) and 3–4 (crude HR 13.80 [95% CI 5.99, 31.80]), respectively (Table 2). Compared with patients with CRB-65 score of 1–2, mortality within 28 days was higher in those with CRB-65 of 3–4 (crude HR 3.18 [95% CI 1.46, 6.89]).
Fig. 2 Kaplan–Meier survival curves (showing cumulative mortality and 95% CI) for COVID-19 patients stratified in terms of FBG or CRB-65 score at admission. (a) Kaplan–Meier survival curves of all COVID-19 patients stratified by FBG; (b) Kaplan–Meier survival curves of all COVID-19 patients stratified by CRB-65 score; (c) Kaplan–Meier survival curves of COVID-19 patients with a CRB-65 score of 0, stratified by FBG; (d) Kaplan–Meier survival curves of COVID-19 patients with a CRB-65 score of >0, stratified by FBG

FBG and CRB-65 score at admission
CRB-65 score is a measure of pneumonia severity. The interaction between trends across FBG and CRB-65 scores did not reach statistical significance (p = 0.1112 for crude and 0.2243 for adjusted analyses). Higher FBG levels were associated with increased mortality in the group with a CRB-65 score of 0 (Fig. 2c, ptrend < 0.0001) and with a CRB-65 score of >0 (Fig. 2d, ptrend = 0.0044). In patients with a CRB-65 score of 0, mortality within 28 days was higher in the group with FBG ≥7.0 mmol/l (crude HR 6.57 [95% CI 2.65, 16.27]) and with FBG 6.1–6.9 mmol/l (crude HR 3.42 [95% CI 1.51, 10.19]) when compared with the group with FBG <6.1 mmol/l, respectively. No statistically significant difference was found between the groups with FBG ≥7.0 mmol/l (crude HR 1.92 [95% CI 0.74, 4.99]) and FBG of 6.1–6.9 mmol/l. In patients with a CRB-65 score of >0, mortality within 28 days was higher in the group with FBG ≥7.0 mmol/l (crude HR 1.99 [95% CI 1.24, 3.20]) compared with FBG <6.1 mmol/l. No statistically significant difference was found between the groups with FBG of 6.1–6.9 mmol/l and FBG <6.1 mmol/l (crude HR 1.44 [95% CI 0.77, 2.70]), or between the groups with FBG ≥7.0 mmol/l and FBG of 6.1–6.9 mmol/l group (crude HR 1.38 [95% CI 0.77, 2.48]).

FBG at admission and complications within 28 days
Then, we analysed the relationship between the FBG and complications in COVID-19 patients. The number of patients who had complications within 28 days in the groups with FBG <6.1 mmol/l, 6.1–6.9 mmol/l and ≥7.0 mmol/l was 86 (14.2%), 48 (7.9%) and 103 (17.0%), respectively. The number of patients without complications within 28 days in the groups with FBG <6.1 mmol/l, 6.1–6.9 mmol/l and ≥7.0 mmol/l was 243 (40.2%), 52 (8.6%), and 73 (12.1%), respectively (Table 1). Compared with patients with admission FBG <6.1 mmol/l, patients with admission FBG ≥7.0 mmol/l (OR 3.99 [95% CI 2.71, 5.88]) and 6.1–6.9 mmol/l (OR 2.61 [95% CI 1.64, 4.41]) had higher levels of in-hospital complications.