Uric acid stones: a study of 58 patients

Uric acid calculi: types, etiology and mechanisms of formation

The study of the composition and structure of 41 stones composed of uric acid was complemented by in vitro investigation of the crystallization of uric acid. Uric acid dihydrate (UAD) precipitates from synthetic urine under physiological conditions when the medium is supersaturated with respect to this compound, though uric acid anhydrous (UAA) represents the thermodynamically stable form. Solid UAD in contact with liquid transforms into UAA within 2 days. This transition is accompanied by development of hexagonal bulky crystals of UAA and appearance of cracks in the UAD crystals. Uric acid calculi can be classified into two groups, differing in outer appearance and inner structure. Type I includes stones with a little central core and a compact columnar UAA shell and stones with interior structured in alternating densely non-columnar layers developed around a central core; both of them are formed mainly by crystalline growth at low uric acid supersaturation. Type II includes porous stones without inner structure and stones formed by a well developed outermost layer with an inner central cavity; this type of stones is formed mainly by sedimentation of uric acid crystals generated at higher uric acid supersaturation.

Urinary lithogenesis in Sudanese patients: a study of stone formers

This prospective study confirms the previously reported high incidence of uric acid lithiasis in the Sudan. Despite this fact urinary pH in patients in whom stones formed was not significantly different from controls (p greater than 0.05). However, a significantly high serum uric acid level (p less than 0.01) was associated with recurrent and/or bilateral stones. In patients with single episodes of stones significant hyponatremia (p less than 0.001) may indicate excessive sweating. The resulting low urine output supersaturated with crystals may explain lithogenesis in this group of patients.