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Editor,—Akçay et al observed a significantly lower urinary citrate excretion in children with a previous history of urolithiasis.1 Their findings are comparable with data presented in adult stone forming patients, showing a high incidence of hypocitraturia.2 As citrate is a potent inhibitor of calcium-oxalate or calcium-phosphate crystal aggregation,3 hypocitraturia is one important factor influencing recurrent urolithiasis.
Urinary citrate excretion, expressed as a citrate/creatinine ratio, in idiopathic stone forming children (n = 25) was compared with the citrate excretion in healthy boys and girls (n = 241 ). Unfortunately the authors did not indicate whether they present amolar creatinine ratio (mol/mol), or a ratio expressed inmg/mg. Therefore, the data are of limited value at present.
We examined urinary citrate excretion in 473 healthy infants and children of different age groups, showing that citrate excretion is not only sex but also age related.4 Mean molar citrate/creatinine ratio was higher (p <0.05) in both male and female infants, than in older age groups; in infancy it was higher in females than in males (1.9 v 0.63 mol/mol, p <0.05). During childhood, girls tended to have slightly lower mean molar ratios than boys (0.27 v 0.33). This relationship changed in adolescence, when girls again had higher mean citrate excretions than boys (0.32 v 0.28 mol/mol), as observed in healthy adults.2
The absence of a relationship between age, gender, and urine citrate excretion in the study of Akçay et al is likely because of an insufficient power to detect such differences.
In conclusion, we look forward to a response from the authors about the unit of the citrate/creatinine ratio. We suggest that there exist normal age and sex related values for citrate/creatinine ratio in infants and children which are based on adequate population data.4 This will allow the clinician to evaluate further idiopathic urolithiasis.
Professor Akçay comments:
We examined the urinary citrate/creatinine ratio in 25 children with idiopathic calcium urolithiasis and in 25 controls. The mean citrate excretion was calculated as citrate/creatinine ratio and we presented a ratio expressed in g/g. The mean (SD) citrate excretion in controls, 0.51(0.2), was significantly higher in patients with urolithiasis, 0.181(0.076).
We couldn’t determine a correlation between urinary citrate excretion and age because the children in our study were of about the same age.
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