Abstract
The measurement of discrete renal functions by means of “clearance” technics has been of great value in the study of both normal and abnormal kidney physiology. However, the technics 1 required for the accurate measurement of glomerular filtration rate, renal plasma flow and tubular function have several disadvantages, especially when applied to human subjects. Since inaccurate collection of urine constitutes the main source of error, an indwelling catheter, bladder washouts, and 3 or more serial collections of urine are required to yield reasonable accuracy. The amount of time devoted to the collection of blood and urine samples and to the chemical analyses prevents the standard method of measurement of the discrete renal functions from being a simple routine clinical procedure.
Several investigators 2 - 3 have devised technics which make the collection of urine unnecessary. These methods depend upon the rate of disappearance of inulin (or mannitol) and diodrast (or p-amino hippuric acid) from the blood after intravenous injection. These technics require serial blood samples to insure accuracy, and are not suitable for repeated observations at intervals of less than one day.
A simple procedure for the measurement. A of glomerular filtration rate and renal plasma flow has been devised that requires only a blankw plasma sample and a single plasma sample for each estimation of the renal functions. This procedure is based on the assumption that, at equilibrium, the amount of a non-metabolized substance injected intravenously per minuteshould equal the amount excreted by the kidney per minute; i.e. providing this is the only excretory route.
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