SIMPLE TESTS OF RENAL FUNCTION USING CREATININE, PHENOLSULPHONPHTHALEIN, AND PITRESSIN.

The reciprocals of the blood urea nitrogen and plasma creatinine levels, the maximum specific gravity of the urine after vasopressin, and three modified forms of the phenolsulphonphthalein (P.S.P.) excretion test were found to be directly related to the glomerular filtration rate (G.F.R.) in hospital patients. From 34 to 75 patients were studied for each test, and in 21 patients all tests were performed concurrently. The plasma creatinine level and the 15-minute urinary excretion of P.S.P. were found to be the most useful simple tests of renal function and gave sufficiently accurate estimates of total function (G.F.R.) to justify their more extensive use. The G.F.R. (ml./min./1.73 sq. m. of body surface area) could be calculated from each test, using the following equations:- [Formula: see text] G.F.R. = 3.15 x P.S.P.% + 19, where P.S.P.% is the 15-minute urinary excretion of P.S.P., expressed as a percentage of the administered dose. Satisfactory estimates of G.F.R. were also given by the simplified relationships [Formula: see text]. In the presence of impaired renal function more accurate estimates of G.F.R. were obtained from the plasma creatinine and P.S.P. excretion tests (S.D. of estimate 8 and 13 ml./min. respectively). It was thought that these tests could well replace the commonly used blood urea nitrogen estimation as simple tests of renal function.