Effect of diet on creatinine clearance and excretion in young and elderly healthy subjects and in patients with renal disease.
Thirty-seven young healthy subjects with normal renal function were studied to assess the quantitative effect of protein intake on creatinine clearance. A standard 24-h urine collection and blood sample at the end of the collection were obtained for creatinine and urea concentrations. Correlations between creatinine clearance and urinary urea nitrogen excretion (r = 0.8; P less than 0.0001) and calculated protein intake (r = 0.8; P less than 0.0001) were observed. A significant relationship between creatinine clearance and urea nitrogen excretion was also demonstrated in 28 elderly healthy subjects and 33 patients with renal disease. To demonstrate a cause and effect between urea nitrogen excretion and creatinine clearance in healthy subjects, 18 of the 37 healthy subjects repeated the 24-h urine collection and blood sample after ingesting 5 g of urea in addition to their usual diet. Mean urinary urea nitrogen excretion increased from a mean value of 9.8 +/- 4.0 to 11.8 +/- 4.0 g/day. There was a strong correlation between the changes in urea nitrogen excretion and the changes in creatinine clearance. In acute studies with oral protein loading, there was a significant correlation between creatinine clearance and urinary urea nitrogen excretion. It was concluded that protein intake has a direct and quantitative effect on creatinine clearance in healthy subjects. In normal humans, it is likely that GFR is not a fixed function. Thus, a low creatinine clearance is not a categorical sign of renal disease. A low creatinine clearance adjusted for urea nitrogen excretion may be a useful clinical tool to assess renal function.
Lew
S W
SW
Department of Medicine, George Washington University Medical Center, Washington, DC.
Bosch
J P
JP
D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001806:Blood Urea Nitrogen; D003404:Creatinine / Q000378:metabolism*; D004044:Dietary Proteins / Q000008:administration & dosage*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007674:Kidney Diseases / Q000178:diet therapy / Q000378:metabolism*; D008297:Male; D008875:Middle Aged
D004044:Dietary Proteins; D003404:Creatinine