Although it has been shown in the preceding paper that the specific gravity of the urine cannot be used as a means to determine the rate of excretion of solids, and although it must be regarded as a very inaccurate method of estimating even that partial function of the kidney by virtue of which it is able to separate a concentrated solution from a blood in which the urinary constituents are relatively dilute, it, nevertheless, remains true that in certain cases specific gravity determinations may give information of considerable clinical value. There is a relation between the inability to produce a urine of high specific gravity and certain extreme grades of renal decompensation. It is this inability which, in certain cases, leads to the constantly low specific gravity in short time urine collections, which is in sharp contrast with the very variable specific gravity of the urine in normal persons.
ADDIS T, SHEVKY MC. A TEST OF THE CAPACITY OF THE KIDNEY TO PRODUCE A URINE OF HIGH SPECIFIC GRAVITY. Arch Intern Med (Chic). 1922;30(5):559-562. doi:10.1001/archinte.1922.00110110030004