Legrand H, et al. - Researchers, herein, report the prevalence of differences between cystatin C-based (eGFR_cys) and creatinine-based (eGFR_creat) estimated glomerular filtration rate (eGFR) in older adults and investigated which subsets of individuals may be most impacted by differing estimations. They found that in the study population, differences between eGFR_creat and eGFR_cys were common and often of large magnitude. In addition, multiple non-GFR determinants were found to be correlated to differences in GFR estimations.