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Byline: A. Edefonti (1), M. Picca (2), B. Damiani (2), S. Loi (2), G. Consalvo (2), M. Giani (2), L. Ghio (2), G. Origgi (3), M. Ferrario (3) Keywords: Key wordsaMeasured nitrogen losses; Chronic peritoneal dialysis; Models predicting nitrogen losses Urinary nitrogen losses; Dialysate nitrogen losses; Fecal nitrogen losses Abstract: To develop models to estimate nitrogen (N) losses of children on chronic peritoneal dialysis (CPD) from easily measurable indexes and laboratory tests, we measured the N content and all nitrogenous compounds in dialysate (D), urine (U), and feces over 3 days in 19 pediatric patients on CPD. Total measured N losses (TNm) were 5.56+-2.26 g/day (69.9+-11.1% in dialysate, 16.3+-10.6% in urine, and 13.6+-4.6% in feces). Correlation coefficients between measured dialysate and urinary N losses and the single nitrogenous compounds indicated values of over 0.9 only for urea in dialysate and urine fecal N losses correlated well with body surface area (BSA). Taking into account these correlations, we developed a univariate additive model and three multivariate models to predict total estimated N losses (TNe). The best prediction of TNm was obtained with model 3, which considered not only urea output in dialysate and urine but also dialysate protein loss and BSA: TNe (g/day)=0.03+1.138 UN urea+0.99 DN urea+1.18 BSA+0.965 DN protein. A confirmatory analysis performed on a second group of 23 pediatric patients on CPD, using all four models, showed a higher percentage of studies with a relative difference between TNm and TNe less than 10% for model 3 than for the other models. Thus, N losses of pediatric patients on CPD can be estimated from measured urea and protein losses in dialysate and urea loss in urine, together with BSA. Author Affiliation: (1) Clinica Pediatrica De Marchi, Via Commenda, 9, I-20122 Milan, Italy Tel.: +39-02-57992451, Fax: +39-02-57992451, IT (2) Pediatric Renal Unit, 2nd Department of Pediatrics, University of Milan Medical School, Milan, Italy, IT (3) Research Center for Chronic Degenerative Diseases, University of Milan, Milan, Italy, IT Article note: Received: 11 October 1999 / Revised: 1 March 2000 / Accepted: 1 March 2000