Blood samples
chronic kidney disease
Participants fasted overnight, and venous blood samples were taken by trained staff and immediately sent to the accredited Laboratory of Clinical Chemistry, Västmanland County Hospital, Västerås. The estimated glomerular filtration rate (eGFR) was calculated from serum creatinine levels standardized by isotope dilution mass spectrometry (Synchron LX or UniCel DxC instruments; Beckman Coulter Inc., Brea, CA, USA) using the chronic kidney disease epidemiology (CKD-EPI) formula.