Crystalline morphology and compositions of melamine-associated urinary stones caused by consumption of melamine-contaminated infant formula are reported.

Twelve melamine-associated urinary stone samples were obtained from 12 children aged from 3 to 36months 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.

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 339,000μg/g. XRD analysis in 6 stone samples showed that amorphous mineral phase was involved in the calculogenesis.

Melamine and uric acid are the main possible etiologic factors closely related to melamine-associated urinary stone formation in humans.