Clinical application of current tests of renal function.

Recent advances in renal physiology and methodology make it possible to assess accurately and quantitatively the discrete excretory functions of the kidney. 1 The functions subject to quantitative measurement are the rate of glomerular filtration, renal blood flow, maximal tubular excretory capacity, and maximal tubular reabsorptive capacity. The rate of glomerular filtration is measured by means of the clearance of inulin, i. e., the amount excreted per minute divided by the plasma concentration represented by the clearance formula UV/P. Since inulin is filtered at the glomerulus and is neither reabsorbed nor excreted by the tubules, the simple clearance calculation indicates the amount of filtrate formed. The mean normal rate of glomerular filtration is 130 cc. per minute. The renal blood flow is measured by means of the clearance of p -aminohippurate. Since this substance is completely removed from the renal arterial blood during one circulation through the kidneys, its clearance