Measurement of Renal Hemodynamics in Man by the "Slope Method" without Urinalysis

Abstract

In 17 expts. on 16 patients "slope clearances" of PAH and mannitol were compared with simultaneously run conventional urine clearances. Both test substances were injd. intraven. in a single injn. The proportion of each disappearing from the plasma per unit of time represents the fraction excreted by the kidney per unit of time, assuming no extra-renal loss. The product of that proportion (S) and the volume of fluid in which the substance is distributed (Vc) is equivalcnt to the volume of fluid that contains the amt. removed by the kidney per unit of time, or the renal "slope clearance" (C = VcS). All urine and plasma specimens were hydrolyzed with HC1 to release conjugated PAH before colorimetric analysis. Values of PAH clearance detd. by the slope method and based on the volume of distribution of either PAH or mannitol, failed to be confirmed consistently by simultaneously measured urine clearances. PAH slope clearance agreed more often with urine clearance when the slope clearance was based on the volume of distribution of mannitol than when based on the volume of distribution of PAH. This agreement occurred too frequently to be fortuitous. Values for mannitol clearance determined by the slope method were consistently lower than simultaneously measured urine clearances; therefore, mannitol cannot be detd. by the slope method.