Abstract
It was recently shown that at low plasma levels about 94% of the phenol red clearance in the normal human kidney is accomplished by tubular activity. 1 In view of this fact this clearance is a sensitive index of tubular excretion, and when observed simultaneously with the inulin clearance, affords evidence of the respective functional activities of the tubules and of the glomeruli. The present investigation concerns the study of these clearances together with the urea clearance in 21 subjects with glomerular nephritis either during a first attack, during an exacerbation, or in the chronic stage.
We have endeavored to maintain the urine flow above the augmentation limit wherever possible so that the urea clearances would be physiologically comparable. The urea clearance has ranged from 64.6 to 5.4, the inulin clearance from 131 to 6.2 cc. per minute; the urea/inulin clearance ratio has ranged from its normal value of 0.55 to a value of 0.88. In no case has the urea/inulin clearance ratio been observed to fall significantly below the normal value in any stage of the disease. In general it tends to rise, so that in advanced chronic glomerular nephritis it has a value of 0.85 or higher. Our observations do not bear out the belief that in renal disease there is increased back-diffusion of urea, or that the elevation of the blood urea is due to such back-diffusion.
A full discussion of the behavior of the phenol red clearance and its relation to the inulin clearance in various stages of disease must be deferred to a later time, but a few interesting features may be noted here. In general, in those individuals in whom renal impairment is not too far advanced, the phenol red/inulin clearance ratia tends to maintain its normal value (above 3.0), suggesting that injury of glomeruli and tubules progresses in a parallel manner, as might be expected from the anatomical structure of the nephron.
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