New aspects on the composition, structure and origin of calcium oxalate monohydrate calculi.

In this paper a thorough study on the composition and structure of calcium oxalate monohydrate (COM) papillary calculi is presented. In 86.4% of these calculi, small amounts of phosphates were detected and generally located at the calculi core. This demonstrates the importance of phosphates as the heterogeneous nucleus of 'pure' COM calculi. Study of the main biochemical parameters of these patients showed that the most frequent biochemical alteration was associated with hypocitraturia (25%), whereas hypercalciuria and/or hyperoxaluria were detected in very few cases. With respect to the urinary pH values, 70% of the patients presented values lower than 6 and 30% higher than 6. These facts indicate that in a number of cases the formation of phosphates is not the result of persistent high urinary pH values, and the presence of occasional papillary microinfections must be suspected. It is clear that, by avoiding the formation of heterogeneous phosphate nuclei, 'pure' COM calculi would not develop, and consequently therapies for these individuals under these conditions must take this into account.