E411 analyzer

Participant age, sex, race, past medical history, and smoking status were obtained by questionnaire at the baseline visit. Blood pressure was measured three times after a 5-minute seated rest using an automated BP device (Model 907; Omron Healthcare), and the mean value was used. Body mass index was calculated as weight in kilograms divided by height in meters squared. Serum PTH was measured using an intact PTH immunoassay (e411 analyzer; Roche, Indianapolis, IN), with an interassay coefficient of variation of 4.9% at 35.1 pg/mL and 2.5% at 210.4 pg/mL, with an analytic measurement range of 1.2–5000 pg/mL.³¹ Fasting serum cholesterol, high density lipoprotein (HDL) cholesterol, creatinine, urine albumin, and urine creatinine were measured at the Central Laboratory on a Roche c501 instrument.^{32 (link)} The CKD Epidemiology Collaboration combined creatinine and cystatin C equation^{23 (link)} was used to estimate GFR.

All covariates were assessed at baseline following standard protocols. BMI was calculated from measured weight and height at both visits and obesity was defined as a BMI ≥ 30 kg/m². Diabetes was defined as fasting (≥8 hours) blood glucose ≥126 mg/dL, non-fasting blood glucose ≥ 200 mg/dL, self-reported physician diagnosed diabetes or “sugar in blood”, or use of medication for diabetes in the past two weeks. Hypertension was defined as mean systolic blood pressure (BP) ≥ 140 mmHg, mean diastolic BP ≥ 90 mmHg, or use of medication for high blood pressure in the past 2 weeks. Atherosclerotic cardiovascular disease (ASCVD) was defined as history of coronary heart disease and/or stroke.
Assays of NT-proBNP levels were conducted in serum (visit 2) and plasma (visit 4) samples that had been stored at −70°C. Measurements were made using a sandwich immunoassay method on a Roche Elecsys 2010 Analyzer at visit 2, and an ECLIA immunoassay on an automated Cobas e411 analyzer at visit 4. The lower detection limit for both assays was 5 pg/mL, and participants with unmeasurable levels were assigned a value of 2.5 pg/mL. NT-proBNP, glucose, total cholesterol, HDL- and LDL-cholesterol, triglycerides and hs-CRP were re-calibrated based on published equations to minimize any systematic differences across study visits (23 (link)).