Assessment of kidney function in adults

Kidney function is typically assessed by measuring the glomerular filtration rate (GFR). Many approaches have been used: accuracy demands complex techniques involving the use of exogenous filtration markers (e.g inulin, iohexol, 99mTc-diethylenetriaminepentaacetic acid, 125I-iothalamate, 51Cr-ethylenediaminetetraacetic acid). For most clinical purposes, accuracy is sacrificed for practicality and a blood marker, creatinine (concentration of which has an inverse relationship to GFR) 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, widespread application of creatinine-based GFR-estimating equations, which aim to circumvent some of the limitations of serum creatinine, has become popular. The most widely used of these is the Modification of Diet in Renal Disease (MDRD) Study equation. 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 protein (or albumin) concentration or excretion. The use of urinary protein:creatinine (or albumin:creatinine) ratios obviates the need for 24-hour urine collections.