Urea Tests of Renal Efficiency. I. by I. M. Rabinowitch

The urea tests of renal efficiency commonly mentioned in the literature include (a) simple estimation of blood urea concentration, (b) determination of urine urea concentration following ingestion of urea, and (c) observations on the relationship between blood and urine urea concentrations. From a comparative study of these three methods, the general conclusion reached in this hospital (1) was that in renal lesions associated with azotemia or any other evidence of impairment in excretion of nitrogenous substances, the ratio of urine urea to blood urea concentration was the most sensitive index of renal efficiency. All urea tests are based upon the clinical observation that when the kidneys become impaired the rate of excretion of urea diminishes. If the rate of excretion cannot keep pace with the rate of production urea accumulates in the blood. Rate of excretion of urea in the urine, and degree of retention of urea in the blood are therefore regarded as indices of kidney function. The assumption that these tests estimate the ability of the kidneys to do work connotes that excretory ability of the kidneys is the only, or at least predominant, factor influencing urea excretion. Ambard, Marshall, and Davis, Pepper and Austin, and Addis and his coworkers have recorded their observations on the effects of blood urea concentration. In 1921, Van Slyke and his COworkers demonstrated the influence of urine volume output (2). For normal individuals these authors presented a mathematical exD pression for the relationship of these factors. Thus, K = m