Measures of Renal Tubular Function
ESTIMATION of the ability of renal tubules to concentrate urine is of as great value as any single test in establishing diagnosis and prognosis cost to the patient and with minimal effort to the examiner. With this to recommend it, the principle should be widely applied.
In the measurement of concentrating ability the aim should be to determine maximal or “ceiling” specific gravity. Possibly because many of the methods suggested do not furnish such values they are infrequently used. General acceptance and usage of a single, practical method of testing for maximal specific gravity might contribute toward more uniformity in the understanding of the various types of renal disease.
The method described by Lashmet and Newburgh1 probably most nearly measures maximal concentrating ability. They proposed that the oral intake of solids be controlled for seven days before and three days during water deprivation. However, the duration and rigorous restrictions of the test make routine application unlikely.
Brunn, 1921; 2 Sodeman and Engelhardt, 1941-1943; 3, 4 and more recently Horne and Morris, 1947, 5 have utilized the antidiuretic principle of posterior pituitary extract as a means of estimating the ability of the kidneys to concentrate urine. After subcutaneous injection of 10 units of surgical pituitrin, they observed a sharp decrease of urinary output and an increase of specific gravity which attained its maximum degree at two hours and persisted for three to four hours. The specific gravities of the specimens collected from normal persons ranged from 1.022 to 1.036 (Sodeman and. . .