Study design and participants
The present study population comes from the China Hypertension Registry Study whose main aim is to establish a national registry of hypertension patients, investigate the prevalence and treatment of hypertension in China. In addition, this observational study plans to evaluate the correlative factors that affect hypertension and its prognosis. Patients were eligible for enrollment if they were 18 years of age or older;had hypertension which defined based on the usual 140/90 mmHg threshold, self-report history of hypertension, or the use of anti-hypertensive drug(s) at baseline; signed informed consent. And if they had psychological or nervous system impairment resulting in an inability to demonstrate informed consent or unable to be followed-up according to the study protocol, or plans to relocate in the near future or those patients who were not suitable for inclusion or for long-term follow-up as assessed by study physicians, they would be excluded. We recruited a total of 14,268 study participants in Wuyuan, Jiangxi Province, China from March 2018 to August 2018. After excluding non-hypertensive, individuals with ABI date missing and AST/ALT date missing, 10,900 subjects included in the analysis finally.
The study was conducted in accordance with the Declaration of Helsinki and was approved by the Ethics Committee of the Anhui Medical University Biomedical Institute. Informed written consent was obtained from all patients before their enrollment in this study.
Measurement of Ankle brachial index (ABI) and assessment of PAD
The resting ABI is the initial diagnostic test for PAD. Systolic blood pressure is measured by Doppler ultrasonography in each arm and in the dorsalis pedis (DP) and posterior tibial (PT) arteries in each ankle using the Omron Colin BP-203RPE III device (Omron Health Care, Kyoto, Japan). The right and left ankle–brachial index values are determined by dividing the higher ankle pressure in each leg by the higher arm pressure. In present study, patients with resting ABI ≤ 0.9 were defined as PAD.
All the study subjects were told one day in advance that fasting venous blood samples would be collected the next morning. After an overnight fast, venous blood samples were obtained from all study participants. Next, the blood samples of all the subjects were collected, frozen and transported to the Biaojia Biotechnology Laboratory for analysis in Shenzhen, China. Serum concentrations of fasting blood glucose (FBG), high-density lipoprotein cholesterol (HDL-C), total cholesterol (TG),triglycerides(TG), low-density lipoprotein-cholesterol (LDL-C), aspartate aminotransferases (AST) and alanine transaminase (ALT), total bilirubin (TBIL), direct bilirubin (DBIL), glutamyltransferase (GGT), albumin (ALB), uric acid (UA), homocysteine(Hcy), creatinine were measured using automatic clinical analyzers (Beckman Coulter, USA) and the laboratory staff were blind to the research protocol. estimated glomerular filtration rate (eGFR) was estimated using the newly developed CKD-EPI equation.
At this baseline assessment, age, smoking, alcohol consumption,medical history (any hypertension, stroke, diabetes, hyperlipidemia and chronic kidney disease) and medication intake (antihypertensive drugs, glucose-lowering drugs, lipid-lowering drugs, antiplatelet drugs) were queried by trained health professionals. Systolic diastolic pressures (SBP, mmHg) and diastolic blood pressure (DBP, mmHg), measured by electronic sphygmomanometers after the subjects had rested for 10 minutes. The anthropometric examinations included weight, height, waist circumference and hip circumference. Body mass index (BMI) was calculated as the body weight in kilograms divided by the square of the height in meters (kg/m2).
In order to investigate whether the AST / ALT ratio of the selected participants is related to PAD, the statistical analysis includes four main steps. First, baseline characteristics of participants according to tertiles of AST / ALT ratio were presented. Continuous variables were expressed as the means ± standard deviations and categorical variables were expressed as a frequency(%). Second, crude and adjusted regression models were used to assess the association between AST/ALT ratio (as continuous variable and categorical variable, respectively) and PAD. Third , generalized additive model (GAM) and smooth curve fitting (penalized spline method) were conducted. Finally, we performed various subgroup analyses.
All data analysis used the statistical package R (https://www.R-project.org, The R Foundation) and Empower (R) (www.empowerstats.com; X&Y Solutions, Inc., Boston, MA) . Two-tailed P < 0.05 was defined as statistically significant.