Estimating glomerular filtration rate for the full age spectrum from serum creatinine and cystatin C

Background. We recently published and validated the new serum creatinine (Scr)-based full-age-spectrum equation (FAS(crea)) for estimating the glomerular filtration rate (GFR) for healthy and kidney-diseased subjects of all ages. The equation was based on the concept of normalized Scr and shows equivalent to superior prediction performance to the currently recommended equations for children, adolescents, adults and older adults. Methods. Based on an evaluation of the serumcystatin C (ScysC) distribution, we defined normalization constants for ScysC (Q(cysC) = 0.82 mg/L for ages< 70 years and Q(cysC) = 0.95 mg/L for ages >= 70 years). By replacing Scr/Q(crea) in the FAS(crea) equation with ScysC/Q(cysC), or with the average of both normalized biomarkers, we obtained new ScysC-based (FAS(cysC)) and combined Scr-/ScysC-based FAS equations (FAS(combi)). To validate the new FAS(cysC) and FAS(combi) we collected data on measured GFR, Scr, ScysC, age, gender, height and weight from 11 different cohorts including n = 6132 unique white subjects (368 children, aged <= 18 years, 4295 adults and 1469 older adults, aged >= 70 years). Results. In children and adolescents, the new FAS(cysC) equation showed significantly better performance [percentage of patients within 30% of mGFR (P30) = 86.1%] than the Caucasian Asian Paediatric Adult Cohort equation (P30 = 76.6%; P< 0.0001), or the ScysC-based Schwartz equation (P30 = 68.8%; P< 0.0001) and the FAS(combi) equation outperformed all equations with P30 = 92.1% (P< 0.0001). In adults, the FAS(cysC) equation (P30 = 82.6%) performed equally as well as the Chronic Kidney Disease Epidemiology Collaboration equation (CKD-EPIcysC) (P30 = 80.4%) and the FAS(combi) equation (P30 = 89.9%) was also equal to the combined CKD-EPI equation (P30 = 88.2%). In older adults, FAS(cysC) was superior (P30 = 88.2%) to CKDEPIcysC (P30 = 84.4%; P< 0.0001) and the FAS(combi) equation (P30 = 91.2%) showed significantly higher performance than the combined CKD-EPI equation (P30 = 85.6%) (P< 0.0001). Conclusion. The FAS equation is not only applicable to all ages, but also for all recommended renal biomarkers and their combinations.