Risk stratification nomogram for diabetic foot ulcer recurrence after healing in type 2 diabetes

Table 1 Baseline characteristics of study population, n (%)/mean ± SD

Variable	All patients (n = 312)	No recurrence (n = 184)	Recurrence (n = 128)	Test statistic	P value
Age, years	64.3 ± 10.8	63.8 ± 11.2	65.1 ± 10.2	t = 0.98	0.328
Male sex	198 (63.5)	114 (62.0)	84 (65.6)	χ2 = 0.42	0.517
Diabetes duration, years	14.0 (10.0-19.0)	12.0 (9.0-17.0)	16.0 (12.0-21.0)	Z = 4.12	< 0.001
Body mass index, kg/m2	27.8 ± 4.3	27.5 ± 4.1	28.2 ± 4.6	t = 1.35	0.178
Current smoking	87 (27.9)	42 (22.8)	45 (35.2)	χ2 = 5.64	0.018
Hemoglobin A1c (%)	7.8 ± 1.4	7.3 ± 1.2	8.5 ± 1.3	t = 7.82	< 0.001
HbA1c ≥ 8.0%	142 (45.5)	62 (33.7)	80 (62.5)	χ2 = 25.3	< 0.001
Serum albumin, g/L	36.8 ± 4.2	38.2 ± 3.7	34.7 ± 4.1	t = 7.45	< 0.001
Serum albumin < 35 g/L	118 (37.8)	52 (28.3)	66 (51.6)	χ2 = 17.2	< 0.001
Peripheral neuropathy score	6.2 ± 2.1	5.4 ± 1.9	7.3 ± 1.8	t = 8.12	< 0.001
Neuropathy score ≥ 7	156 (50.0)	68 (37.0)	88 (68.8)	χ2 = 31.5	< 0.001
Peripheral arterial disease	164 (52.6)	74 (40.2)	90 (70.3)	χ2 = 27.9	< 0.001
ABI	0.94 ± 0.21	1.02 ± 0.18	0.82 ± 0.19	t = 8.93	< 0.001
ABI < 0.9	147 (47.1)	58 (31.5)	89 (69.5)	χ2 = 44.2	< 0.001
Previous ulcer duration > 8 weeks	136 (43.6)	52 (28.3)	84 (65.6)	χ2 = 43.1	< 0.001
Inadequate offloading compliance	143 (45.8)	56 (30.4)	87 (68.0)	χ2 = 43.7	< 0.001

HbA1c: Hemoglobin A1c; ABI: Ankle brachial index.

Table 2 Univariable Cox proportional hazards regression analysis

Variable	Hazard ratio (95%CI)	P value
Age (per 10-year increase)	1.08 (0.92-1.27)	0.342
Male sex	1.16 (0.79-1.70)	0.452
Diabetes duration (per 5-year increase)	1.24 (1.11-1.39)	< 0.001
Current smoking	1.68 (1.15-2.45)	0.007
HbA1c ≥ 8.0%	2.53 (1.74-3.68)	< 0.001
Serum albumin < 35 g/L	2.18 (1.51-3.14)	< 0.001
Peripheral neuropathy score ≥ 7	2.94 (2.02-4.28)	< 0.001
Peripheral arterial disease	3.21 (2.19-4.70)	< 0.001
ABI < 0.9	3.15 (2.16-4.59)	< 0.001
Previous ulcer duration > 8 weeks	3.68 (2.52-5.37)	< 0.001
Inadequate offloading compliance	3.42 (2.34-5.00)	< 0.001

HbA1c: Hemoglobin A1c; ABI: Ankle brachial index.

Table 3 Multivariable Cox proportional hazards regression analysis

Variable	Hazard ratio (95%CI)	P value
Previous ulcer duration > 8 weeks	3.24 (2.15-4.88)	< 0.001
Peripheral arterial disease	2.87 (1.92-4.29)	< 0.001
Inadequate offloading compliance	2.73 (1.82-4.09)	< 0.001
ABI < 0.9	2.56 (1.71-3.83)	< 0.001
Peripheral neuropathy score ≥ 7	2.45 (1.63-3.68)	< 0.001
HbA1c ≥ 8.0%	2.18 (1.46-3.25)	< 0.001
Serum albumin < 35 g/L	1.92 (1.28-2.88)	0.002

HbA1c: Hemoglobin A1c; ABI: Ankle brachial index.

Table 4 Model performance metrics

Metric	Training cohort (n = 218)	Validation cohort (n = 94)
C-index (95%CI)	0.832 (0.789-0.875)	0.826 (0.787-0.865)
Sensitivity at 1 year	82.3%	80.6%
Specificity at 1 year	78.9%	77.4%
Positive predictive value	74.2%	73.1%
Negative predictive value	85.7%	84.3%
Calibration slope	0.98	0.96
Calibration intercept	0.02	0.04

CI: Confidence interval.

Table 5 Risk stratification groups and recurrence rates

Risk group	Point range	1-year recurrence rate	2-year recurrence rate
Low risk	0-100	8.1% (4.2%-12.0%)	12.3% (7.5%-17.1%)
Intermediate risk	101-180	28.4% (22.1%-34.7%)	38.7% (31.8%-45.6%)
High risk	> 180	58.9% (51.2%-66.6%)	71.2% (63.8%-78.6%)