Sir.—The widespread use of dipsticks such as the Ames N-Multistix-SG strip (Miles Laboratories, Elkhart, Ind) has some built-in problems as well as a form of medical laboratory absurdity. Comments have been made in the more general literature, but to date we have not read a comment in a pediatric journal.
I refer specifically to the use of the term specific gravity that one reads from these strips. The measurement of specific gravity in urine has been used in clinical medicine for a number of years with known advantages and disadvantages. One advantage is that in the absence of albumin and glucose, the specific gravity has a nearly linear correspondence to osmolality over the range of interest to the clinician. This correlation enables one to detect the ability of the kidney to concentrate and dilute, which is a sensitive measure of renal function. This usefulness is lost if there is
SCHAEFFER A. Interpretation of Specific Gravity by Dipstick. Am J Dis Child. 1988;142(6):592. doi:10.1001/archpedi.1988.02150060026016