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Age-related values of 123I-orthoiodohippurate (OIH) single kidney clearance rate (Cl) were estimated in a large cohort of likely normal children aged between 0 and 18 years. Among 4,111 children examined in the past 10 years, 917 were selected with the following inclusion criteria: (a) mild ultrasonographic hydronephrosis with right differential renal function (DRF) <53% and >47% (498 pts), (b) known or suspected urinary tract infection with normal ultrasound, serum creatinine and DMSA and DRF <53% and >47% (419 pts). 123I-OIH-Cl was assessed using a validated gamma camera method. Children were divided into 21 age classes: from 0 to 2 years, eight 3-month classes; from 2 to 14 years, twelve 1-year classes; from 14 to 18 years, one 4-year class. Cl, plotted against age, was fitted using an increasing function ( % MathType!Translator!2!1!AMS LaTeX.tdl!TeX -- AMS-LaTeX! % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbbjxAHX % garmWu51MyVXgatuuDJXwAK1uy0HwmaeHbfv3ySLgzG0uy0Hgip5wz % aebbnrfifHhDYfgasaacH8qrps0lbbf9q8WrFfeuY-Hhbbf9v8qqaq % Fr0xc9pk0xbba9q8WqFfea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qq % Q8frFve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeWaeaaakeaaca % WG5bGaeyypa0JaamyyaiabgkHiTiaadkgacaWGLbGaeyOeI0Iaam4y % aiaadIhaaaa!400A! $$y = a - be - cx$$ ). Mean 123I-OIH-Cl of 1,834 kidneys was 306±22 ml/min/1.73 m2 BSA. Mean 123I-OIH-Cl of the right and left kidneys was 307±23 and 305±22 ml/min/1.73 m2 BSA, respectively ( p<0.002). The best-fitting 123I-OIH-Cl growing function was: Cl=311−230 e−0.69×Age (months). 123I-OIH-Cl improved progressively starting from birth, reaching 96% and 98% of the mature value at 1 and 1.5 years, respectively. 123I-OIH-Cl at birth (age=0) was 81 ml/min/1.73 m2 BSA. After 18.6 days of life, the renal function had doubled its starting value, and it reached a plateau of 311 ml/min/1.73 m2 BSA at 2 years. This work represents a systematic evaluation of ERPF by a gamma camera method in a large cohort of selected likely normal paediatric subjects. [ABSTRACT FROM AUTHOR]