The Effect of Urine Volume on Urea Excretion

Abstract

In recent papers Bing (1) and Williams (2) have proposed formulae which these authors believe to be more accurate than the original "standard" and "maximum" clearance equations of M6ller, McIntosh, and Van Slyke (3,4), in expressing the effects of urine volume flow on the urea clearance in human subjects. Both Bing and Williams base their formulae on the data of M6ller et al (3).The essential test of accuracy of such a formula is the consistency with which it permits one to calculate, from clearances shown by a subject with widely varying urine flows, the clearance that he would show with a given constant urine flow. Neither Williams nor Bing has applied such a test. In the present paper it is applied to compare their formulae with the original equations of Miller et al, with data from both normal and nephritic subjects. The theoretically derived equation of Dole (5), which was apparently overlooked by both Williams and Bing, is also included in the comparison, and tentative conclusions are drawn concerning permeability changes in the renal tubules in chronic nephritis.CLEARANCE FORMULAE Maximum and standard clearance formulae of Austin et al (6), and M6ller et al (3). Simultaneous observations of urea excretion rates, urine volumes, and blood urea concentrations made by Austin et al (6) and by MBller, et al (3) showed that the urea clearance, defined as the volume of blood containing the amount of urea excreted in 1 minute, was but little affected by urine flow changes in normal human subjects when the flow (per 1.73 sq. m. body area) exceeded an "augmentation limit" which was usually about 2 cc. per minute, but that when the urine flow fell below this limit the urea clearance fell with the urine flow, the clearance then becoming proportional approximately to the square root of the flow. Chesley (7,8) confirmed the square root rule for urine flows down to about 0.35 cc. per minute, but found that when extreme dehydration reduced urine flow below this rate, further reduction in flow was accompanied by a more rapid fall in urea clearance, which then fell in direct proportion to the urine flow, rather than to its square root.The above empirically observed effects of urine volume on the urea clearance in the 3 respective urine flow ranges are expressed by Equations 1, 2 and 3, in which C. represents the clearance calculated as UVIB, for any urine volume flow V (in cc. per minute), and U and B indicate the concentrations of urea in urine and blood respectively. When V exceeds the augmentation limit of about 2:1. C, = Cm = constant for each subject.Cm is the "maximum clearance" of M6ller et al (3), and averages 75 for normal adults.' When V is between the augmentation limit and 0.5 cc.per minute:2. C, = C, fV- 3. C. = Rm X V. Rm is a constant, the maximum U/B ratio attainable by decreasing urine flow to its minimum. The average normal value of Rm is about 75. (In nephritis the value of Rm may fall to 3 or 4 (9) and be reached with urine volumes above 1 cc. per minute [see Table IV is made by using as V corrected, t...

Fractional Excretion of Urea as a Guide to Renal Dysfunction

“…These authors concluded that the patients had a low FEUr due to increased urea reabsorption at the collecting duct. It has also been established that an increase in urine volume alone can increase FEUr [16][17][18][19][20][21][22]. At least 2 of our patients (patient 3: table 1; patient 6: table 2).…”

The Significance of the Urea Clearance

“…Factors Affecting Clearance Like all physiological functions, the urea clearance varies under different physiological conditions, particularly those which affect the renal blood flow (Van Slyke et al, 1934, 1935 and the urine volume (Van Slyke, 1947;Moller et al, 1928;Dole, 1943). Consequently the clearance of a given subject may vary by as much as ±20 % of his average under the usual conditions of daily life (Moller et al, 1928).…”

“…Renal disease affects as a rule chiefly the rate of filtration, which decreases as glomerular destruction advances, although in advanced nephritis increased permeability of the tubules appears to add its effect by increasing urea reabsorption, particularly when urine volume is low (Van Slyke, 1947). Damage to the tubules by nephrotoxic substances (Richards, 1929;Lucke, 1946), or by renal ischaemia, such as occurs in severe and prolonged shock (Phillips et al, 1946;Van Slyke, 1948;Phillips et al, 1948) appears to make the tubules more permeable to back diffusion of urea into the blood, and lowers the clearance by increasing urea reabsorption.…”

“…Damage to the tubules by nephrotoxic substances (Richards, 1929;Lucke, 1946), or by renal ischaemia, such as occurs in severe and prolonged shock (Phillips et al, 1946;Van Slyke, 1948;Phillips et al, 1948) appears to make the tubules more permeable to back diffusion of urea into the blood, and lowers the clearance by increasing urea reabsorption. In all these conditions the urea clearance has been found of value in assisting the appraisal of the extent of renal damage, and the course of progress either towards recovery or fatal renal failure.…”

The Use of Vaginal and Rectal Cultures in the Management of Gonorrhoea in the Female

“…Thomas and Meyer (1945) carried out four examinations of the urethral and cervical secretions by .smears and cultures on alternate days, starting the day following the completion of treatment. Van Slyke and Heller (1945) insisted on a minimum of ten days' post-treatment observation including at least three negative cultures. These periods refer only to the surveillance for gonorrhoea as distinct from the serological observation to detect incubating syphilis.…”