Assessment of kidney function in adults

Kidney function is typically assessed by measuring the glomerular filtration rate (GFR) and many approaches have been used. Accuracy demands complex techniques involving the use of exogenous filtration markers (e.g. inulin, iohexol, 51Cr-ethylenediaminetetraacetic acid). For most clinical purposes accuracy is sacrificed for practicality and a blood marker, creatinine is used. Serum (or plasma) creatinine has many limitations as a kidney function test, being affected by a variety of non-renal and analytical factors. Serum cystatin C measurement has been proposed as an alternative marker. Recently, application of creatinine-based GFR-estimating equations has become widespread as they adjust for some of the limitations of serum creatinine as a marker of GFR. Estimation of GFR facilitates detection and management of chronic kidney disease and allows disease to be categorized according to an international staging system. In addition to GFR, detection of kidney disease typically involves measurement of urinary albumin (or protein) concentration. The use of urinary albumin:creatinine (or protein:creatinine) ratios obviates the need for 24-hour urine collections.