Laboratory Testing and Clinical Diagnosis

Fasting blood glucose (FBG), 2-hour blood glucose (OGTT 2-hPG), serum TG, total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C) and HDL-C levels were measured using an automatic biochemical analyser (BS180 analyzer, Mindray, Shenzhen, China). HbA1c in venous blood samples was measured using high-performance liquid chromatography (HPLC) (BioRad VARIANT II haemoglobin analyser). Thyroid stimulating hormone (TSH), thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TgAb) were measured using electrochemical luminescence immunoassays (Cobasc601 analyser, Roche Diagnostic, Switzerland). When the TSH level exceeded the upper limit of the reference range (0.27-4.20 mIU/L), free thyroxine (FT4) was measured. FT4 and free triiodothyronine (FT3) were measured when TSH levels were lower than the lower limit of the reference range. UIC was measured using inductively coupled plasma mass spectrometry (ICP-MS) (Agilent 7700x, Agilent Technologies, USA).

According to the International Diabetes Federation (IDF) consensus worldwide definition of the metabolic syndrome promulgated in 2005 in combination with the actual situation of the Chinese population, metabolic syndrome was diagnosed when 3 or more of the following criteria were present: ① abdominal obesity (male waist ≥90 cm, female waist ≥85 cm); ② hypertriglyceridemia (TG≥1.7 mmol/L (150 mg/dL)); ③ low HDL-C (< 1.0 mmol/L in males, < 1.3 mmol/L in females); ④ hypertension (the presence of any of the following 3 conditions was defined as abnormal blood pressure: (a) antihypertensive treatment, (b) systolic blood pressure (SBP) 130 mmHg or higher, or (c) diastolic blood pressure (DBP) ≥85 mmHg); and ⑤ hyperglycaemia (the presence of any of the following 3 conditions was defined as abnormal blood glucose: (a) a self-reported diabetes history or hypoglycaemic treatment, (b) fasting plasma glucose (FPG) ≥5.6 mmol/L (100 mg/dL), (c) OGTT 2-hPG ≥7.8 mmol/L (140 mg/dL), or (d) HbA1c ≥5.7%) (18, 19).