Risk factors and a predictive model of diabetic foot in hospitalized patients with type 2 diabetes

Table 1 Baseline characteristics of the studies population and hazard ratio (95% confidence interval) of univariate Cox model for new-onset diabetic foot, n (%)

Variables	Without diabetic foot (n = 6226)	Incident diabetic foot (n = 75)	HR (95%CI)	P value
Demographic indicators
Age, year	63.0 ± 11.4	67.0 ± 10.1	1.03 (1.01-1.05)	0.006
Sex
Male	3491 (56.1)	42 (56.0)	Reference	-
Female	2735 (43.9)	33 (44.0)	1.02 (0.65-1.61)	0.935
Clinical characteristics
DM duration
< 10 years	3571 (57.3)	21 (28.0)	Reference	-
10-19 years	1797 (28.9)	30 (40.0)	2.58 (1.48-4.51)	0.001
≥ 20 years	858 (13.8)	24 (32.0)	4.49 (2.50-8.07)	< 0.001
Insulin application	3277 (52.6)	56 (74.7)	2.90 (1.72-4.88)	< 0.001
Hyperlipidemia	775 (12.5)	9 (12.0)	0.87 (0.44-1.75)	0.705
Hypertension	3966 (63.7)	59 (78.7)	2.01 (1.16-3.49)	0.013
Stroke	1372 (22.0)	25 (33.3)	1.86 (1.15-3.00)	0.012
Ischemic heart disease	2732 (43.9)	42 (56.0)	1.57 (1.00-2.48)	0.051
Lower extremity arterial disease	210 (3.4)	15 (20.0)	8.06 (4.57-14.20)	< 0.001
Chronic venous insufficiency of the lower extremities	190 (3.1)	3 (4.0)	1.35 (0.43-4.28)	0.612
Diabetic nephropathy	356 (5.7)	20 (26.7)	6.31 (3.78-10.50)	< 0.001
Peripheral neuropathy	595 (9.6)	12 (16.0)	1.88 (1.01-3.49)	0.045
Retinopathy	512 (8.2)	11 (14.7)	2.01 (1.06-3.82)	0.032
Behavior and habits
Smoking	1893 (31.9)	25 (33.8)	1.10 (0.68-1.78)	0.697
Alcohol drinking	2050 (34.5)	22 (29.7)	0.82 (0.50-1.34)	0.426
Physical examination
BMI, kg/m2	21.6 ± 3.3	21.5 ± 2.8	0.99 (0.90-1.10)	0.863
SBP, mmHg	142.0 ± 21.0	143.7 ± 23.9	1.00 (0.99-1.02)	0.502
DBP, mmHg	80.8 ± 12.5	80.1 ± 12.3	1.00 (0.97-1.02)	0.738
Laboratory indicators
FPG, mmol/L	8.3 ± 3.2	10.1 ± 4.6	1.13 (1.08-1.19)	< 0.001
Plasma fibrinogen, g/L	3.0 ± 1.0	3.5 ± 1.3	1.47 (1.25-1.72)	< 0.001
Hemoglobin, g/L	135.5 ± 20.2	127.0 ± 25.4	0.98 (0.97-0.99)	< 0.001
RDW-CV, %	12.7 ± 1.2	13.0 ± 1.2	1.18 (1.05-1.32)	0.005
Lymphocyte count, 109/L	1.9 ± 0.7	1.7 ± 0.7	0.69 (0.48-0.98)	0.037
WBC, 109/L	7.1 ± 2.6	8.1 ± 3.6	1.12 (1.06-1.18)	< 0.001
Albumin, g/L	42.4 ± 5.1	38.6 ± 6.3	0.90 (0.87-0.93)	< 0.001
Serum creatinine, μmol/L, median (IQR)	66.0 (55.0-79.0)	77.0 (54.5-130.0)	1.01 (1.00-1.01)	< 0.001
Alanine aminotransferase, U/L, median (IQR)	16.6 (12.1-24.8)	13.8 (11.1-21.6)	0.97 (0.95-0.99)	0.022
Serum aspartate aminotransferase, U/L, median (IQR)	17.8 (14.6-22.9)	16.5 (14.3-20.8)	0.98 (0.96-1.01)	0.115
Total bilirubin, μmol/L	11.6 ± 6.7	9.7 ± 4.2	0.93 (0.88-0.98)	0.010
Indirect bilirubin, μmol/L	7.1 ± 4.2	5.7 ± 2.9	0.87 (0.80-0.95)	0.001
Serum uric acid, μmol/L	302.7 ± 90.0	311.0 ± 118.4	1.00 (0.99-1.01)	0.418

The characteristics are presented as the mean ± standard deviation if they were normally distributed, or medians (interquartile ranges) if they were not normally distributed. BMI: Body mass index; CI: Confidence interval; DBP: Diastolic blood pressure; DM: Diabetes mellitus; FPG: Fasting plasma glucose; HR: Hazard ratio; IQR: Interquartile range; RDW-CV: red blood cell distribution width coefficient of variation; SBP: Systolic blood pressure; WBC: White blood cell.

Table 2 The predictive model of new-onset diabetic foot over the whole follow-up period in hospitalized patients with type 2 diabetes

Variable	HR (95%CI)	P value
Diabetes duration
< 10 years	Reference	-
10-19 years	1.86 (1.05-3.28)	0.032
≥ 20 years	2.96 (1.63-5.39)	< 0.001
Albumin	0.91 (0.88-0.95)	< 0.001
FPG
4.4-6.9 mmol/L	Reference	-
< 4.4 mmol/L	3.99 (1.55-10.25)	0.004
≥ 7.0 mmol/L	3.12 (1.66-5.87)	< 0.001
Diabetic nephropathy	2.23 (1.25-3.99)	0.007
Lower extremity arterial disease	6.21 (3.44-11.24)	< 0.001

CI: Confidence interval; HR: Hazard ratio; FPG: Fasting plasma glucose.

Table 3 The predictive model of new-onset diabetic foot over the whole follow-up period in hospitalized patients with type 2 diabetes using a down-sampling approach

Variable	Sampled population, n = 5301		Sampled population, n = 4301		Sampled population, n = 3301		Sampled population, n = 2301
	HR (95%CI)	P value	HR (95%CI)	P value	HR (95%CI)	P value	HR (95%CI)	P value
Diabetes duration
< 10 years	Reference	-	Reference	-	Reference	-	Reference	-
10-19 years	1.87 (1.03-3.39)	0.041	1.80 (0.95-3.41)	0.072	2.68 (1.20-6.00)	0.016	3.45 (1.22-9.75)	0.019
≥ 20 years	2.42 (1.25-4.69)	0.008	1.93 (0.92-4.06)	0.082	2.31 (0.89-5.99)	0.085	2.65 (0.79-8.88)	0.113
Albumin	0.92 (0.88-0.96)	< 0.001	0.93 (0.89-0.97)	0.001	0.92 (0.87-0.96)	0.001	0.91 (0.86-0.97)	0.006
FPG
4.4-6.9 mmol/L	Reference	-	Reference	-	Reference	-	Reference	-
< 4.4 mmol/L	3.92 (1.43-10.74)	0.008	4.31 (1.45-12.80)	0.008	6.94 (1.84-26.17)	0.004	7.65 (1.87-31.29)	0.005
≥ 7.0 mmol/L	2.70 (1.40-5.24)	0.003	2.40 (1.19-4.86)	0.014	3.68 (1.41-9.56)	0.008	3.41 (1.13-10.22)	0.029
Diabetic nephropathy	2.47 (1.32-4.64)	0.005	2.96 (1.49-5.89)	0.002	3.30 (1.51-7.22)	0.003	3.48 (1.36-8.94)	0.009
Lower extremity arterial disease	5.15 (2.66-9.96)	< 0.001	3.84 (1.74-8.46)	0.001	3.28 (1.23-8.79)	0.018	4.34 (1.52-12.40)	0.006

The predictive Cox model adjusted diabetes duration, diabetic nephropathy, and lower extremity arterial disease as covariates. CI: Confidence interval; FPG: Fasting plasma glucose; HR: Hazard ratio.