UroToday - Borawski, et al in the January 2008 issue of The Journal of Urology collected 24-hour urine samples from 48 healthy subjects with no history of stone disease, endocrine abnormalities, or urological surgeries over a three and a half year period. All the children were toilet trained and age 3 to 18 years of age. The 24-hour urine samples were evaluated for urinary calcium, oxalate, uric acid, citrate, magnesium, sodium, phosphorus, and potassium levels. They were all adjusted for urinary creatinine. Also, in a separate analysis of these 24-hour urine samples, urine chemistries were adjusted for body weight in kilogram.

The groups were divided into 4 age groups; group 1 (3 to 5 years old), group 2 (6 to 10 years), group 3 (11 to 15 years), and group 4 (16 to 18 years).

The group found that urinary pH and volume decreased with increasing age, although the difference in pH did not reach statistical significance. When the urine samples had unadjusted urinary parameters they failed to show statistical difference among the age groups. When they were adjusted for urinary creatinine and body weight all the urinary parameters including calcium, oxalate, uric acid, citrate, magnesium, sodium, phosphorus, and potassium decreased with increasing age. These were all statistically significant except for calcium itself.

From their study the group concluded that differences exist, not only between adults and children for normal urinary metabolic parameters but also among different age groups within the pediatric population. They go on to further state that stone risk factors in 24- hour urine samples decrease with increasing age in healthy, non-stone forming children.

Urinary reference values for stone risk analysis is children is playing a crucial role in the care of this patient population. Only recently has it become adopted in very few laboratory values. Although noted in the study that nephrolithiasis is a relatively rare occurrence in the pediatric population, it is on the rise. They state that 7% of stone disease in North America will be found in children younger than 16 years of age. We have noticed a rise in our practice here at The Children's Hospital of Philadelphia with seeing over 1600 patients with stone disease over the past 3 years. There was an editorial comment at the end of this paper by Julian Wan from Ann Arbor, Michigan. Dr. Wan states that the main flaw with the paper, which was acknowledged by the authors, is that the sample size is very small. I agree with Dr. Wan that it would be extremely useful to perform a multi centered analysis with a large cohort of patients, hopefully numbering in the thousands so we can get a study with enough power to truly state normal values and parameters for our pediatric patients.

Borawskia KM, Sura RL, Miller OF, Pake CYC, Premingera GM, Kolon. TF

J Urol. 179(1): 290-294, January 2008

10.1016/j.juro.2007.08.163

Reported by UroToday Contributing Editor Pasquale Casale, M.D

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