Clinical characteristics of refractory melamine-related renal calculi

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.

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.

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).

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.