Some Observations on the Urea Concentration Test.

Abstract

Some observations on the phenolsulphonephthalein excretion and urea concentration of the urine in 49 students are here briefly reported. The urea concentration test was carried out entirely as described by MacLean and de Wesselow. 1 The phenolsulphonephthalein tests were carried out in the usual manner, the dye being injected intravenously in all cases and colors matched without the aid of a colorimeter. All the students examined were normal, healthy adults between the ages of 20 and 30. Urinalysis was negative in all cases.

The maximum urea concentration of the urine varied from 2.4% to 4.1%. In 45 of 49 students the concentration varied from 2.5% to 4.0%. The average was 3.22%. Phenolsulphonephthalein excretion varied from 43% to 82.5% with an average of 66.3%.

When the results of the 2 tests in each case are compared a great variation is noted. Curves of phenolsulphonephthalein excretion and the corresponding maximum urea concentration (with the individual determinations arranged in the order of the phenolsulphonephthalein excretion), do not coincide, as they should if they were both quantitative indicators of the excreting power of the kidneys.

In comparing the results of these 2 tests, it must, of course, be remembered that whereas in the dye test the total amount of that dye excreted in 2 hours is measured, in the second test the concentration of urea in a varying amount of urine is determined. This fact is recognized in MacLean's instructions that specimens of 120 cc. or over should be discarded as the dilution of the urea is in such cases too great to be reliable. Curves of volume of urine, plotted in relation to the corresponding urea concentration, indicate that the amount of urine, even when only quantities less than 120 cc. are considered, influences the reading more than has heretofore been recognized.