Characterization of melamine-associated urinary stones in children with consumption of melamine-contaminated infant formula

Background: Crystalline morphology and compositions of melamine-associated urinary stones caused by consumption of melamine-contaminated infant formula are reported. Methods: Twelve melamine-associated urinary stone samples were obtained from 12 children aged from 3 to 36 months who were treated in Lanzhou University Second Hospital. The crystalline morphology and compositions of these stone samples were analyzed using a combination of infrared spectrum, SEM and XRD. The presence of melamine in 12 stones was determined by HPLC Results: Diversity of crystalline morphology in 10 stone samples was revealed by SEM observation. Infrared spectral data revealed that 8 of the 10 stone samples predominantly consisted of the crystal forms of urate: 1 of sodium urate monohydrate, 2 of uricite and 5 of uric acid dihydrate and ammonium urate. However, ammonium magnesium phosphate hexahydrate, ammonium urate and carbonate apatite were also identified in 1 stone sample. The content of melamine in all of the 12 stone samples was determined by HPLC and found to range from 200 to 339,000 mu g/g. XRD analysis in 6 stone samples showed that amorphous mineral phase was involved in the calculogenesis. Conclusions: Melamine and uric acid are the main possible etiologic factors closely related to melamine-associated urinary stone formation in humans. (C) 2012 Elsevier B.V. All rights reserved.