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To the Editor:—
Dr. Sumner Marshall, in "Urea-Creatinine Ratio in Obstructive Uropathy and Renal Hypertension" (JAMA190:719 [Nov 23] 1964), indicated that an increased ratio of urea to creatinine differentiated obstructive urinarytract disease from inherent renal disease causing azotemia. In my experience, no such differentiation can be made. In acute renal insufficiency from many causes and in acute obstructive processes, blood urea nitrogen (BUN) rises precipitously in comparison to the creatinine. However, after many weeks or months, plasma creatinine also rises to decrease the original dissociation. Thus, it is simply a matter of the rapidity of the renal damage and the timing of the tests. Because of the slow endogenous production of creatinine, plasma creatinine levels increase much more slowly than urea levels with either type of renal damage. An increase in the ratio of urea to creatinine only means a rapid type of renal insufficiency, obstructive or otherwise.
Harrow BR, Marshall S. Urea-Creatinine Ratio. JAMA. 1965;191(8):678–679. doi:10.1001/jama.1965.03080080068028
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