Advia 1650

Although the diagnosis of renal impairment in clinical practice is based on the finding of a decrease in the glomerular filtration rate (GFR) and/or on the detection of elevated urinary excretion of albumin [3 (link)], we defined renal impairment as the estimated GFR (eGFR) ≤ 60 mL/min/1.73 m², as in other studies, due to lack of urinary microalbumin concentration data during 2008–2010 and 2015–2017 [15 (link), 16 (link)].
Serum creatinine was measured by a colorimetric method (ADVIA1650, Siemens, USA) before 15 February 2008 and by the Jaffe rate-blanked and compensated method (Hitachi Automatic Analyzer 7600, Hitachi, Tokyo, Japan) after 20 February 2008. eGFR was calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation [17 (link)].

All study participants were asked to fast for at least 8 h the day before blood collection. Between 8 a.m. and 10 a.m., a clinical pathologist collected 15 mL of blood from the participants’ forearms vein using a spasm blood collection tube and needle. The collected blood was then centrifuged at 3000 rpm for 10 min, using a Combi-514R (Hanil, Seoul, Republic of Korea), with the serum being used for analysis.
Total cholesterol (TC) and triglycerides (TGs) were analyzed via enzyme colorimetry using automatic analyzers and the contained reagents from Siemens (ADVIA-1650; Norcross, GA, USA). High-density lipoprotein (HDL) and low-density lipoprotein (LDL) cholesterol were also analyzed via the elimination/catalase method, using the ADVIA-1650 system (Siemens, Berlin, Germany) in accordance with the manufacturer instructions.

All participants were questioned about lifestyle factors, including alcohol consumption and smoking. Alcohol consumption was defined as drinking alcohol more frequently than once per week. Smoking was defined as current cigarette smoking.
Anthropometric measurements were made by a single examiner. After a 10-minute resting period, blood pressure was measured in the sitting position. Body mass index was calculated as weight (kg) divided by height squared (cm²).
Abdominal fat tissue area was calculated using computed tomography (Tomoscan 350; Philips, Mahwah, NJ, USA) as described previously [21 (link)].
Blood samples were collected after at least an 8-hour overnight fasting period. Fasting glucose, high sensitive C-reactive protein (hs-CRP), total cholesterol, triglyceride, and high-density lipoprotein (HDL) cholesterol levels were measured using an ADVIA 1650 chemistry system (Siemens Medical Solution, Tarrytown, NY, USA). Fasting insulin levels were determined using electrochemiluminescence immunoassays with an Elecsys 2010 (Roche, Indianapolis, IN, USA). Insulin resistance was calculated using the homeostasis model assessment of insulin resistance (HOMA-IR) index: (insulin [μIU/mL] × fasting blood glucose [mg/dL]/18)/22.5.

All subjects were surveyed for their age, sex, marital status, smoking, drinking, and other habits. Blood pressure, height, weight, waist circumference and hip circumference were measured according to standard protocols, as previously reported [22 (link)]. Body mass index (BMI) was calculated as the weight divided by the square of height. Obesity was defined with BMI ≥25kg/m², according to the Asian-specific BMI cut-off from the World Health Organization Report [25 ]. For biochemical tests, when participants visited for their follow-up examinations, blood was collected after the subjects had fasted for at least 8 hours. Biochemical data including glucose, HDL, LDL, triglyceride, and hsCRP levels were measured (ADVIA 1650 and 1680, Siemens, Tarrytown, NY, USA). Body composition was measured by means of multi-frequency bioelectrical impedance analysis (BIA) with 8-point tactile electrodes (InBody 720; Biospace, Seoul, Korea) [26 (link), 27 (link)]. This analyzer uses an alternating current of 250 mA at variable frequencies of 1, 5, 50, 250, 500, and 1,000 kHz. Fat-free mass and fat mass were obtained from a multi-frequency BIA.

After an overnight fast, a total sample of at least 19 cc of blood was drawn into a serum separator tube (SST) and two ethylenediamine-tetra-acetic acidtubes and placed into a conical tube for laboratory tests and storage. The biospecimens were given study IDs that were matched to the participants’ questionnaires and labeled with 2D bar code stickers. Biospecimens are kept in refrigerators at each medical institution until they are collected within 24 h by a courier from the commercial laboratory that processes specimens using various laboratory tests^{21 (link)}. Blood test results were uploaded to the Korean Centers for Disease Control (KCDC) web-based database system. The extracted samples were subsequently transported to and stored at the National Biobank of Korea (https://biobank.nih.go.kr/eng). Baseline SUA, hs-CRP, fasting blood glucose (FBG), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), alanine aminotransferase (ALT), aspartate aminotransferase (AST), creatinine, and gamma glutamyl transferase (GGT) levels were measured using enzymatic calorimetric methods with automatic analyzers (ADVIA 1650 and ADVIA 1800 (Siemens, Tarrytown, NY, USA)²⁴ . Quality control of biospecimens in the Biobank of Korea has been described in detail elsewhere^{25 ,26 (link)}.

The laboratory tests were performed in two steps. First, on the day of clinical evaluation, participants were asked to have a twelve hour fasting period and to come to the Sleep Clinic at 8:00 AM for blood sample collection for hemogram, creatinine, urea, glycemia, lipid profile, and hepatic function measures. The biochemical profile and the hepatic function measures were performed by an automated assay (ADVIA 1650, Siemens), and the hemogram was performed by microscopic and automated methods (ADVIA 120, Siemens).
One week later, participants returned to the Sleep Clinic for determination of urinary, plasma and platelet catecholamine. They were asked to abstain from a hypercaloric diet, alcohol, caffeine, chocolate, carbonated beverages, and tea three days before collection of blood and 24-hour urine [32] . Blood samples for plasma and platelet catecholamine measurements were obtained from an antecubital vein. The samples were collected in the morning at 9 AM, after a 12-hour fasting period and 1 hour of rest. Twenty four hour urine was collected from participants and then acidified with 5 mL of 6N HCl prior to the tests [33] (link).