Phenol Red Clearances in Man

Abstract

Although phenol red, introduced by Rowntree and Geraghty in 1912, has been widely used as an empirical renal function test in man, there is no information on the excretion of this substance in relation to the simultaneous excretion of other urine constituents.∗ With knowledge available concerning the order of magnitude of glomerular filtration in man, 1 a determination of phenol red clearance is of particular interest in indicating the relative rôle played by filtration and secretion in the excretion of this substance.

Preliminary observations following oral, intramuscular and intravenous administration of phenol red indicate that the latter is most suitable for investigative purposes. In the observations reported here, a sterile 10% solution of the dye, prepared for us by Hynson, Westcott and Dunning, was administered intravenously following the intravenous administration of inulin, and the experiments were so conducted that the simultaneous clearances of inulin and phenol red could be determined at various plasma levels of the latter, standard (basal) physiological conditions being maintained throughout. The dose of phenol red was varied from 300 mg. to 5 gm. per man, and observations were made at plasma concentrations ranging from 0.1 to 28.2 mg. %.

At plasma levels of the dye below 1.5 mg. %, the phenol red clearance is essentially constant, having an average value of about 400 cc. per minute, when calculated upon the total dye in the plasma. The phenol red/inulin clearance ratio averages about 3.2 under these conditions. A series of such observations on several individuals are recorded in the upper right hand corner of Fig. 1. As the plasma level of the dye is increased, the phenol red clearance is lowered both absolutely and relative to the inulin clearance, until the phenol red/inulin clearance ratio may be less than 1.00. This depression of the phenol red clearance appears to be reversible, the same results being obtained, whether an intermediate plasma concentration is reached by the administration of a small dose, or on a falling plasma curve after the administration of a large dose. Results obtained in two series of observations on one individual (L.R.) are recorded in the figure.