Abstract
The multitude of substances whose “clearances”, or rate of excretion in relation to blood concentration, have been proposed as tests of kidney function indicates that a satisfactory clinical procedure is yet to be devised. The use of urea, as proposed by Moller, McIntosh and Van Slyke, 1 is in our experience the simplest of the more sensitive tests, since it involves only one blood sample and does not require the ingestion of the test substance. But since the rate of urea excretion is less with low urine volume than with high, function tests can be compared only as a percentage of an average empirical normal for urine volumes above or below 2 cc. per minute. There are, therefore, certain advantages in using a test substance whose excretion is independent of urine volume. Creatinine, the use of which was proposed by Rehberg, 2 is such a substance. This method as described 3 has the disadvantage of requiring ingestion of creatinine, and analysis of urine and 2 samples of blood plasma.
The development by Van Slyke and Cope 4 of a clinical method for the determination of urea clearances suggested that a similar procedure might be devised for the creatinine clearance which, if practical, would considerably simplify the test.
In the method of Van Slyke and Cope, the ratio between urine and blood urea concentrations is determined by a direct comparison, without determining the actual concentration in either. In the method here described, the same principle is applied except that creatinine is used. In order to increase the concentration of creatinine in the blood and urine, creatinine is administered to the subject by mouth, and water given at hourly intervals during the test if there is any question of the subject's ability to urinate.
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