Assessing Kidney Function

Kidney function is largely defined by GFR. Using GFR to characterize CKD requires an understanding of its physiological variation as well as its decline with healthy aging. The measurement of GFR is based on the urinary or plasma clearance of an ideal or near ideal exogenous marker such as inulin or iothalamate. This requires infrastructure, expense, and patient burden that are not feasible in most clinical settings. Endogenous markers cleared primarily by glomerular filtration, particularly serum creatinine, are more practical and useful to detect loss of kidney function. Estimated GFR can improve the interpretation and application of endogenous filtration markers as GFR. However, estimated GFR still reflects non-GFR biology of the underlying markers. There is not one GFR estimating equation that accurately estimates GFR in all clinical settings, optimally predicts CKD outcomes, and performs the same as measured GFR in its association with CKD risk factors and outcomes.