Evidence for impaired assimilation of protein in chronic renal failure.
BACKGROUND
Protein malnutrition is a common finding in chronic renal failure (CRF) and is associated with poor outcome. We hypothesized that besides inadequate dietary protein intake and alterations in metabolism, deficient protein assimilation (digestion and absorption) might contribute to the pathogenesis of protein malnutrition in uremia.


METHODS
Protein assimilation was evaluated in 64 healthy volunteers and 119 CRF patients by means of a 13C protein breath test and/or quantification of p-cresol in a 24-hour urine collection. Both approaches provide reliable information on the efficiency of protein assimilation. Breath test results were expressed as maximum percentage of administered dose of 13C (%max) and cumulative percentage at the end of the test (%cum(end)). Data were stratified according to renal function.


RESULTS
As compared to subjects with glomerular filtration rate (GFR) > or = 60 mL/min/1.73 m2, subjects with GFR < 30 mL/min/1.73 m2 demonstrated significantly lower breath test-derived parameters of protein assimilation (%max 3.97 +/- 0.23 vs. 5.20 +/- 0.23, P=0.0017; %cum(end) 13.91 +/- 0.86 vs. 17.40 +/- 0.80, P= 0.013) and significantly higher urinary output of p-cresol (54.88 mg/24 hours vs. 28.65 mg/24 hours, P= 0.0005). %max (r=0.399, P < 0.0001), %cum(end) (r=0.347, P=0.0007), and urinary p-cresol (r=-0.229, P=0.007) correlated significantly with GFR. Serum albumin correlated significantly with %max (r=0.399, P=0.0002), %cum(end) (r=0.408, P=0.0001), and urinary p-cresol output (r=-0.186, P=0.035).


CONCLUSIONS
Our data provide evidence that protein assimilation is impaired in CRF. This impairment might contribute to protein malnutrition in CRF.
Bammens
Bert
B
Department of Medicine, Division of Nephrology and Laboratory of Radiopharmaceutical Chemistry, University Hospital Gasthuisberg, Leuven, Belgium.
Verbeke
Kristin
K
Vanrenterghem
Yves
Y
Evenepoel
Pieter
P
D000042:Absorption; D000328:Adult; D000368:Aged; D001944:Breath Tests; D002247:Carbon Isotopes; D003408:Cresols / Q000652:urine; D003430:Cross-Sectional Studies; D004063:Digestion; D004527:Egg Proteins / Q000378:metabolism* / Q000493:pharmacokinetics; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007676:Kidney Failure, Chronic / Q000150:complications / Q000378:metabolism* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D011502:Protein-Energy Malnutrition / Q000209:etiology; D012709:Serum Albumin / Q000032:analysis
D002247:Carbon Isotopes; D003408:Cresols; D004527:Egg Proteins; D012709:Serum Albumin; C032538:4-cresol