Supplementary Material for: Glomerular Filtration Rate in Healthy Living Potential Kidney Donors: A Meta-Analysis Supporting the Construction of the Full Age Spectrum Equation

<p><b><i>Background:</i></b> Normal kidney function or, more specifically, normal glomerular filtration rate (GFR) in men and women and its decline with age is still much debated today. The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation has gender (and race) multiplication factors, accounts for a decline that starts at very young age and assumes that the mean GFR is as high as 120-130 ml/min/1.73 m<sup>2</sup> from a young age. The full age spectrum (FAS) estimated mean GFR is about 107 ml/min/1.73 m<sup>2</sup> at a young age and remains constant until the age of 40 years and then starts to decline both in men and women. The aim of this research study was to give more insight into ‘normal' GFR levels and the physiological decrease of kidney function with age and to use a meta-analysis to evaluate the mathematical construction of the FAS and the CKD-EPI equation. <b><i>Methods:</i></b> We conducted a meta-analysis of published GFR measurements in healthy Caucasian living potential kidney donors (n = 5,482, 46.8% men). Only publications dating from 2000 were selected to avoid the possible influence of body surface area changes in the last decades on the indexed GFR, expressed in ml/min/1.73 m<sup>2</sup>. <b><i>Results:</i></b> We found that the mean GFR ≈ 107 ml/min/1.73 m<sup>2</sup> up to the age of 40 years, but renal decline begins beyond 40 years. No evidence could be found for any difference between men and women in the separate age groups. <b><i>Conclusions:</i></b> The current meta-analysis supports the mathematical form of the FAS equation, which matches the age/sex dependency of measured GFR for healthy potential living kidney donors.</p>