THE PHENOL RED CLEARANCE IN NORMAL MAN

Abstract

In normal men the phenol red clearance is considerably in excess of the simultaneous inulin clearance. The phenol red/inulin clearance ratio is essentially constant at plasma levels of the dye below 1.0 mgm. %, and averages 3.2. As the concn. of dye in the plasma is increased, the absolute phenol red clearance is depressed, as is also the phenol red/inulin clearance ratio (the inulin clearance remaining unaffected). Phenol red is bound by proteins in human plasma, and thus rendered unavailable for filtration, the fraction of free phenol red varying with the absolute concn. of the dye. It is estimated that under the conditions examined here (as also under the conditions of the standard phenol red test) not over 6% of the excreted dye is excreted by glomerular filtration. Phenol red, when added to human blood, is confined to the plasma. To effect the phenol red clearance observed at low plasma levels (400 cc. per minute) a blood flow of at least 700 cc. per min. is required.