Objective: The melamine urinary stones are uric acid-based and amenable to alkalization and extracorporeal shock-wave lithotripsy (ESWL). However, a significant percentage of stones failed in alkalization and ESWL. To predict it before a likely deemed failed treatment, we attempt to confirm their clinical characteristics.
Methods: A total of 6 refractory- and 9 sensitive-melamine-related renal calculi were included from 15 children (age 6-51 months, mean 14). Renal function, and blood calcium and uric acid level were measured before treatment. Stone composition was determined qualitatively using Fourier transform infrared. Stone computed tomography (CT)-attenuation value, stone melamine and cyanuric acid level, and stone calcium level were performed quantitatively using spiral CT, high-performance liquid chromatography, and flame atomic absorption spectrum, respectively.
Results: Blood biochemical parameters in all children within the normal reference range and no difference was observed between refractory melamine stones and sensitive melamine stones (P >.05). Compared with sensitive melamine stones, stone calcium level and stone CT-attenuation value in refractory melamine stones were significantly higher (21.58 ± 5.76% vs 1.37 ± 1.47%, P = .000; 1037 ± 341HU vs 156 ± 61HU, P = 0.000). Multivariate regression analysis indicated stone calcium level had more impact on alkalization failure than other factors (P(children's age) = .670, P(feedingtime) = .826, P(stonesize) = .376, and P(stonecalcium level) = .000, and P(regressionmodel) = .000).
Conclusion: Higher stone calcium level is the essential change of refractory melamine stones. The stones from children older than 2 years or stones with in vivo CT-attenuation value >700 Hounsfield units in clinical setting should be strong suspected for alkalization- and ESWL-resistance because they most likely contain >10.88% calcium level.
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