2.1 Study populations
A retrospective analysis was performed on 955 patients with DF hospitalized in the endocrinology department of the Air Force Medical Center, PLA from December 2016 to April 2021. Participants included 692 males and 263 females. All the included subjects met the definition of DF established by the World Health Organization in 1999: “In patients with diabetes mellitus, infection, ulceration, and/or deep tissue destruction of the lower extremity are caused by the concomitant neuropathy and various degrees of vascular diseases”[7]. Amputation of a toe or half foot as a consequence of DF surgery or excision of a necrotic limb due to local irreversible gangrene is diagnostic criteria for small amputation. The diabetic foot was graded after the wound was examined using the Wagner classification of diabetic foot, which is as follows[8]:
(1) Grade 0: No open lesions; may have deformity or cellulitis.
(2) Grade 1: Superficial diabetic ulcer (partial or full thickness).
(3) Grade 2: Ulcer extension to the ligament, tendon, joint capsule, or deep fascia without abscess or osteomyelitis.
(4) Grade 3: Deep ulcer with abscess, osteomyelitis, or joint sepsis.
(5) Grade 4: Gangrene localized to the portion of the forefoot or heel.
(6) Grade 5: Extensive gangrenous involvement of the entire foot.
The exclusion criteria were as follows:
(1) Patients who are unable to complete relevant examinations; (2) Patients with liver and kidney dysfunction; (3) Patients with acute complications of DM; (4) Pregnant and lactating women; (5) Patients with malignant tumors;
2.2 Data collection
2.2.1 The general information: gender, age, body mass index (BMI), smoking history, Drinking history, hypertension history, hyperlipidemia history, coronary heart disease history, duration of diabetes mellitus, duration of diabetes foot, peripheral arterial disease (PAD), Diabetic peripheral neuropathy (DPN), diabetic retinopathy (DR) and diabetic nephropathy (DN).
2.2.2 Laboratory inspection: glycerogelatin hemoglobin (HbA1c), fasting plasma glucose (FPG), vitamin D, total cholesterol(TC), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), alanine aminotransferase (ALT), aspartate aminotransferase (AST), Blood urea nitrogen (BUN), Serum creatinine (Scr), serum uric acid (SUA), albumin (ALB), white blood cell count (WBC) and hemoglobin (Hb). After fasting for 8 hours, blood samples were drawn from the patients. All blood biomarkers were tested in the same laboratory.
2.2.3 Relevant clinical examination: Toe-Brachial Index (TBI) and Ankle Brachial Index (ABI). TBI Detection Method: TBI was measured using the network arteriosclerosis detection equipment BP-203RPE III (Omron, Japan). The subject was measured while laying calmly for 10 to 15 minutes. A small cuff was tied at the brachial artery and the thumb of the bilateral upper arm of the patient, and relevant parameters were input, and the instrument automatically calculated TBI. The low values in the left and right sides of the patient were taken at the patient's TBI, and TBI<0.7 was regarded as the outlier[9]. ABI detection methods are as follows: ABI of all patients was detected by color Doppler ultrasonography with a probe frequency of 8-10 MHz. The probe was placed in the pulse position of the patient at an Angle of 45°-60° from the skin, and the probe was moved until the clearest signal was presented. When the blood flow signal disappeared, the cuff was progressively inflated until the pressure was more than 20 mmHg (1 mmHg=0.133 kPa), and then gently deflated and the blood pressure was measured when the blood flow signal reappeared. The blood pressure of both arms was measured and the systolic blood pressure on the higher side was taken as the upper arm systolic blood pressure. The mean blood pressure of the ipsilateral posterior tibial artery and dorsal foot artery was taken as the ankle systolic blood pressure. ABI= ankle systolic blood pressure/upper arm systolic blood pressure. ABI < 0.9 was considered as abnormal ABI.
2.3Statistical analyses
SPSS Statistics 23.0 software packages were used to conduct the data analysis. Variables with normal distribution were expressed as mean ± standard deviation, and the t test was used to compare the two groups. Variables with non-normal distribution were expressed as median (quartile spacing), and the non-parametric Mann–Whitney U-test was used for comparison between the groups. Counting data were expressed as a percentage. Comparison between the two groups was conducted by x2 test. The independent factors were analyzed by binary logistic regression. Before regression analysis, the independent variables of non-normal distribution were transformed by square root or logarithm. P < 0.05 was considered statistically significant.