Procedures for collecting and processing baseline blood and urine samples have previously been reported and validated.19 (link) Biochemical assays were conducted at a dedicated central laboratory. The estimated glomerular filtration rate (eGFR) was calculated using the chronic kidney disease epidemiology collaboration equation.20 (link)Detailed information on covariates was available through standardized questionnaires, including age, sex, race, education, smoking, diet, sleep, mental health, income, and the usage of antihypertensive, cholesterol-lowering, and glucose-lowering medications. Body mass index (BMI) was calculated as weight divided by height squared. Area-based socioeconomic status was derived from the postal code of residence by using the Townsend deprivation score. Baseline prevalent diabetes was identified through multiple procedures considering the type of diabetes and sources of the diagnosis.21 (link) Blood pressure was measured twice manually (manual sphygmometer) or automatically (Omron HEM-7015IT digital blood pressure monitor), and the mean value of the two measurements was used to minimize measurement error.
The details about these measurements can be found in the UK Biobank online protocol (www.ukbiobank.ac.uk).