Urea and nitrogen excretion in pediatric peritoneal dialysis patients.
BACKGROUND
Adequate nutrition is critical to the care of children with end-stage renal disease, and failure to reach the target dietary intake is associated with growth failure. Prospective studies of urea and nitrogen output in adults have led to the derivation of quantitative relationships, which allow assessment of dietary protein intake when only urea appearance is known. Such a clinically useful relationship has not been defined in children receiving chronic peritoneal dialysis (PD).


METHODS
We studied 18 pediatric PD patients (ages 0.8 to 14.3 years) on 132 occasions and determined norms of urea nitrogen appearance (UNA), total nitrogen appearance (TNA), and nonurea nitrogen appearance (NUNA). We stratified data on UNA, TNA, NUNA, nonprotein nitrogen appearance, and the protein equivalent of nitrogen appearance by age groups (0 to 5, 6 to 10, and 11 to 15 years of age) and demonstrated significant differences. In addition, dietary protein and energy intake were measured in the outpatient setting with food scales and dietitian interviews, and the results were stratified by age, presence of residual renal function, and recombinant human growth hormone (rhGH) therapy.


RESULTS
UNA (3.05 +/- 1.38 g/day, 103 +/- 42 mg/kg/day) and TNA (4.67 +/- 1.86 g/day, 159 +/- 52 mg/kg/day) varied significantly between different age groups. NUNA in pediatric subjects (56 +/- 24 mg/kg/day) was significantly greater than previously published adult norms. A linear relationship was defined between UNA and TNA that was specific to pediatric PD patients [TNA (g/day) = 1.26(UNA) + 0.83]. When the relationship was scaled to body mass, the y intercept was significantly different in the youngest subjects [TNA = 1.03 (UNA) + 0.02 (weight in kg) + 0.56 (for subjects age 0 to 5) or 0.98 (for subjects age 11 to 15 or 6 to 10), r2 = 0.91]. Dietary protein intake was significantly greater in subjects receiving rhGH therapy, although nitrogen excretion was unchanged.


CONCLUSIONS
Markers of protein metabolism in pediatric PD patients are age dependent and differ from adult values. An age-specific relationship between TNA and UNA is defined for pediatric subjects; it does not vary with rhGH or the presence of residual renal function.
Mendley
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SR
University of Maryland School of Medicine, Baltimore, Maryland 21201-1595, USA. smendley@peds.umaryland.edu
Majkowski
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NL
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D001835:Body Weight; D002648:Child; D002664:Child Nutritional Physiological Phenomena; D002675:Child, Preschool; D005260:Female; D019382:Human Growth Hormone / Q000008:administration & dosage; D006801:Humans; D007223:Infant; D007676:Kidney Failure, Chronic / Q000178:diet therapy / Q000378:metabolism* / Q000628:therapy*; D008297:Male; D009584:Nitrogen / Q000378:metabolism*; D015596:Nutrition Assessment; D010530:Peritoneal Dialysis; D014508:Urea / Q000378:metabolism*
D019382:Human Growth Hormone; D014508:Urea; D009584:Nitrogen