The Kidney Disease Improving Global Outcomes 2012 Clinical Practice Guideline on Chronic Kidney Disease (1) recommends calculating estimated glomerular filtration rate (eGFR) using equations developed by the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) for adults ≥18 years (2) and by the Chronic Kidney Disease in Children (CKiD) for ages <18 years (3). These equations were recommended because they used readily available information, serum/plasma/blood creatinine, plus age, sex, and race for adults, and height for children; and have been validated in large and diverse cohorts of people who had measured glomerular filtration rate (mGFR) as a basis for establishing accuracy.