Use of Phenol Red in the Addis Test of Renal Function.

Abstract

Under certain special conditions the rate of urea excretion in the urine is directly proportional to the blood urea concentration so that the ration Urine rate/Plasma concentration Becomes a constant. 1 Under these conditions this ratio varies only with the amount of functioning renal tissue 2 , 3 and can be used as an accurate method for measuring renal function in man. 4 It has recently been shown 5 in the rabbit that phenol red is excreted in a manner similar to urea in so far as the relation of the urine rate to the plasma concentration is concerned. This has led us to examine the possibility of using phenol red in place of urea in performing the Addis test of renal function 4 which has been referred to. The results presented in Table I which were obtained from a subject without renal disease after the injection of 1 gm. phenol red∗ during an urea diuresis indicate that it may be feasible to use phenol red in place of urea to determine the Addis excretory ratio. The difference between the urea and phenol red ratios which is apparently constant will be discussed elsewhere. There are certain advantages over urea in the use of the dye, particularly in the determinations in the plasma and urine. The actual concentrations need not be measured. After appropriate dilution and alkalinization the serum and plasma are compared in the 2 cups of a good colorimeter and the ratio calculated from the readings and respective dilutions. The clinical application of the use of phenol red in this manner is being investigated.