Using Glomerular Filtration Rate Estimating Equations: Clinical and Laboratory Considerations

Glomerular filtration rate (GFR)3 estimating equations, infrequently used just a decade ago, are now recommended for the evaluation of kidney function for routine clinical care and are routinely reported by the vast majority of clinical laboratories (1). Current clinical guidelines recommend estimated GFR (eGFR) based on serum creatinine (eGFRCr) as the initial diagnostic test, and either a measured clearance or estimated GFR based on serum cystatin C or the combination of serum cystatin C and creatinine (eGFRCys and eGFRCr-Cys, respectively) as a confirmatory test (2, 3). These recommendations apply to all adults, irrespective of geographic region or clinical presentation.According to the guidelines, measurement of serum concentrations of creatinine and cystatin C should use assays traceable to international reference measurement procedures and materials, and estimation of GFR should use equations developed by the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI), specifically the 2009 creatinine equation and the 2012 cystatin C and creatinine–cystatin C equations, unless other equations have been found to be more accurate in the population of interest (Table 1) (4–6). The rationale for these recommendations is as follows.View this table:Table 1. Endogenous filtration markers and CKD-EPI GFR estimation equations recommended by 2012 KDIGO guidelines for use in adults.First, serum creatinine concentration is routinely measured in clinical practice, and most commercial creatinine measurement procedures are now well standardized; thus eGFRCr is available for use as an initial diagnostic test in most clinical encounters in adults. On the other hand, the international reference standard for cystatin C has been developed only recently, and not all commercial assays are sufficiently well standardized for routine clinical use (7, 8). Second, the CKD-EPI equations can be computed from variables that are generally available in clinical and laboratory information systems (age and sex in addition to serum …