Pediatr Nephrol (2007) 22:514–520 DOI 10.1007/s00467-006-0383-0 ORIGINAL ARTICLE Normative data on the Bonn Risk Index for calcium oxalate crystallization in healthy children Tadeusz Porowski & Walentyna Zoch-Zwierz & Anna Wasilewska & Anthony Spotyk & Jerzy Konstantynowicz Received: 25 July 2006 / Revised: 26 October 2006 / Accepted: 27 October 2006 / Published online: 10 January 2007 # IPNA 2007 Abstract Bonn Risk Index (BRI) is being used for the assessment of urinary calcium oxalate (CaOx) crystalliza- tion. There are no published data regarding BRI during growth. The objective of this study was to establish age- and sex-dependent BRI values in healthy children and adolescents. A total of 1,050 Caucasian subjects aged 3– 18 years (525 males, 525 females) without a history of kidney stone disease were enrolled in the cross-sectional study. The study group was divided into 15 ranges according to age, each comprising 70 subjects. Urinary ionized calcium [Ca2+] was measured using a selective electrode while the onset of spontaneous crystallization was determined using a photometer and titrating with 40 mmol/L ammonium oxalate (Ox2−). The calculation of BRI value was based on the ratio of [Ca2+] to the required amount of ammonium oxalate added to 200 ml of urine to induce crystallization. The median BRI was 0.26 1/L and the values of the 5th and 95th percentiles were 0.06 1/L and 1.93 1/L, respectively. BRI correlated positively with body- area-related BRI (1/L × 1.73 m2) (R = 0.18; P < 0.05), where- as a negative correlation was found between BRI and body T. Porowski (*) : W. Zoch-Zwierz : A. Wasilewska First Department of Pediatrics, Medical University of Bialystok, Children’s Hospital, 17 Waszyngtona St., 15-274 Bialystok, Poland e-mail: tporowski@biaman.pl A. Spotyk Department of Nuclear Medicine, Medical University of Bialystok, Bialystok, Poland J. Konstantynowicz Department of Pediatrics and Auxology, Medical University of Bialystok, Bialystok, Poland weight (1/L × kg) (R = −0.85; P < 0.05). Neither sex nor age differences were detected in BRI across studied children and adolescents. The values of Bonn Risk Index were constant during growth and there was a limited influence of age and sex on BRI in children over 3 years of age. The BRI may be valuable in the evaluation of pediatric patients at risk for kidney stones, particularly if the BRI from stone formers is demonstrated to be higher than in normal children. Keywords Bonn Risk Index (BRI) . Children . Normative values . Oxalate crystallization Abbreviations AP activity product BMI Body Mass Index BRI Bonn Risk Index [Ca2+] ionized calcium concentration CaOx calcium oxalate (Ox2−) amount of ammonium oxalate added to 200 ml of urine to induce crystallization Introduction Urolithiasis is a frequently reported condition in children and is diagnosed even in neonates and infants [1, 2]. The disease may be the first sign of congenital and acquired metabolic disturbances, or the consequence of anatomic or genetic abnormalities [2]. The majority of kidney stones are composed of calcium oxalate and calcium phosphate [1]. Insight into this pathology is increasing and is focused on the pathogenesis of deposit formation in the urinary tract [3–5]. Investigation is being conducted into more effective