Effect of diet on creatinine clearance and excretion in young and elderly healthy subjects and in patients with renal disease

• Published in: Journal of the American Society of Nephrology 1991-10, Vol.2 (4), p.856-865
• Main Authors: Lew, S W, Bosch, J P
• Format: Article
• Language: English
• Subjects: Adult; Age Factors; Aged; Aged, 80 and over; Blood Urea Nitrogen; Creatinine - metabolism; Dietary Proteins - administration & dosage; Female; Glomerular Filtration Rate; Humans; Kidney Diseases - diet therapy; Kidney Diseases - metabolism; Male; Middle Aged
• ISSN: 1046-6673
• DOI: 10.1681/asn.v24856

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.