2.2 Clinical and biochemical measurement
A standardized questionnaire was used to collect baseline data, and was
administered by trained interviewers during a face-to-face interview.
Information collected included lifestyle factors, socio-demographic
characteristics, and family history. Current smoking and drinking status
were divided into 3 groups: never, ever (the cessation of smoking and
drinking for more than half a year), and current (smoking or drinking
regularly in the recent half year). The frequency and duration of
physical activity were obtained using the International Physical
Activity Questionnaire (IRAQ), and the level of physical activity was
evaluated by calculating the metabolic equivalent hours per week
(MET-h/week).
Anthropometrical examinations were conducted by trained staff using
standard protocols. Body weight and height were measured with subjects
wearing light indoor clothing without shoes, and recorded to the nearest
1.0 kg and 0.1 cm, respectively. Body mass index (BMI) was calculated as
weight in kilograms divided by height in meters squared
(kg/m2), and BMI was used to define obesity. Obesity
was defined as a BMI ≥ 28.0 kg/m2, and overweight when
24.0 kg/m2 ≤ BMI < 28.0
kg/m2. Waist circumference (WC) was measured at the
umbilical level to the nearest 0.1 cm with subjects in the standing
position using a non-elastic measuring tape. Central obesity was defined
as a WC ≥ 90 cm in men and ≥ 80 cm in women. Blood pressure was obtained
with the subject seated 3 consecutive times at 5 minutes intervals using
an automated electronic device (OMRON, Omron Company, Dalian, China).
The average of the 3 measurement was used in the analysis. Hypertension
was defined as a systolic blood pressure (SBP) ≥ 140 mmHg or a diastolic
blood pressure (DBP) ≥ 90 mmHg or the subject reporting that they were
receiving regular anti-hypertensive treatment
After an overnight fast of at least 10 hours, venous blood samples were
collected and stored at 80 ºC until testing. All patients also received
a 2h OGTT. Measurements of FPG, 2h OGTT, fasting serum insulin, total
cholesterol (TC), triglycerides (TG), low-density lipoprotein
cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C),
aspartate aminotransferase (AST), alanine aminotransferase (ALT), and
γ-glutamyltransferse (γ-GGT) was done using an automated electronic
device (Beckman CX-7 Biochemical Autoanalyzer, Brea, California, USA).
HbA1c was measured by high-performance liquid chromatography (BioRad,
Hercules, CA). HOMA-β was calculated using the formula: HOMA-β = 20 ×
(fasting plasma insulin, μU/mL) / (FPG, mmol/L) – 3.5. HOMA-IR was
calculated using the formula: HOMA-IR = (FPG, mmol/L) × (fasting plasma
insulin, μU/ml) / 22.518. The abbreviated
Modification of Diet in Renal Disease (MDRD) formula recalibrated for
the Chinese population was used to calculate the estimated glomerular
filtration rate (eGFR) expressed as mL/min per 1.73
m2. The formular is: eGFR = 175 × (serum creatinine ×
0.011)-1.234 × (age)-0.179 × (0.79
if female), with serum creatinine was expressed as μmol/L. Diabetes was
diagnosed according to the 1999 WHO diagnostic criteria, the level of
FPG ≥ 7.0 mmol/L or the level of 2h OGTT ≥ 11.1 mmol/L19.