Role of uric acid in different types of calcium oxalate renal calculi.

OBJECTIVE

The presence of uric acid in the beginning zone of different types of 'pure' calcium oxalate renal calculi was evaluated with the aim of establishing the degree of participation of uric acid crystals in the formation of such calculi.

METHODS

The core or fragment of different types of 'pure' calcium oxalate renal calculi was detached, pulverized and uric acid extracted. Uric acid was determined using a high-performance liquid chromatography/mass spectrometry method.

RESULTS

In calcium oxalate monohydrate (COM) papillary calculi with a core constituted by COM crystals and organic matter, 0.030+/-0.007% uric acid was found in the core. In COM papillary calculi with a core constituted by hydroxyapatite, 0.031+/-0.008% uric acid was found in the core. In COM unattached calculi (formed in renal cavities) with the core mainly formed by COM crystals and organic matter, 0.24+/-0.09% uric acid was found in the core. In COM unattached calculi with the core formed by uric acid identifiable by scanning electron microscopy (SEM) coupled to X-ray microanalysis, 20.8+/-7.8% uric acid was found in the core. In calcium oxalate dihydrate (COD) unattached calculi containing little amounts of organic matter, 0.012+/-0.004% uric acid was found. In COD unattached calculi containing little amounts of organic matter and hydroxyapatite, 0.0030+/-0.0004% of uric acid was found.

CONCLUSIONS

From these results it can be deduced that uric acid can play an important role as inducer (heterogeneous nucleant) of COM unattached calculi with the core formed by uric acid identifiable by SEM coupled to X-ray microanalysis (these calculi constitute the 1.2% of all calculi) and in COM unattached calculi with the core mainly formed by COM crystals and organic matter (these calculi constitute the 10.8% of all calculi).