Variables with P < 0.1 [age, BMI, systolic blood pressure (SBP), severe DFUs, severe PAD, eGFR, ALB, Hb, cerebrovascular disease, diabetic retinopathy and diabetic peripheral neuropathy] in the unadjusted Cox regression analysis (Additional file 2: Table S1), were included as confounding variables in the multivariable cox regression analyses. This evidence concerns the gene GSTM1 and diabetic retinopathy.