This investigation was undertaken to determine whether the changes in blood urea concentration following the ingestion of urea could be utilized in the estimation of kidney function. Certain properties of urea, which are generally recognized, make this substance suitable for such purposes.
Urea is extremely soluble. It is rapidly absorbed unchanged from the gastro-intestinal tract.1
It is distributed in uniform concentration in practically all the tissues of the body.2
It is nontoxic even in large doses.3
Urea is a normal metabolite and a natural stimulus to the kidneys in direct proportion to its concentration in the blood.4
The determination of blood urea nitrogen is simple and accurate.
Under normal conditions, urea is excreted chiefly by the kidneys; elimination through the intestine and skin being negligible.1
There is some evidence indicating that urea is more than an inert excretory product of nitrogen metabolism. The addition of urea to perfusion
KING SE. THE UREA TOLERANCE TEST: AN INDEX OF RENAL FUNCTION. Arch Intern Med (Chic). 1928;42(6):877–892. doi:10.1001/archinte.1928.00130230079007
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