Estimating and measuring glomerular filtration rate: methods of measurement and markers for estimation

Glomerular filtration rate (GFR) is the best overall measure of kidney function. Reference GFR measurements (e.g. inulin clearance) are laborious. Estimation of GFR using equations based on endogenous filtration markers is simpler, cheaper and easy to apply in practice but suffers from limited accuracy and reproducibility. This review summarizes the recent studies comparing measured and estimated GFR in various populations and disease settings. We consider the utility of newer estimating equations based on standardized methodology, including those incorporating cystatin C.

Equations proposed by the Chronic Kidney Disease-Epidemiology (CKD-EPI) Consortium slightly improve the accuracy of GFR estimation compared with those used formerly. The black ethnicity coefficient in the CKD-EPI equation may not be transferable across other black populations and the equations require further validation in other ethnic groups. All currently reported equations fall short of ideal. Incorporation of cystatin C into the CKD-EPI equation improves precision and offers hope of a GFR estimate that may not require ethnic adjustment.

The ideal biomarker and equation to estimate GFR would provide reproducible and accurate results across the entire range of GFRs, populations and diseases. Newer GFR markers and equations are required to fulfil this holy grail of research.