Monosodium Urate in Urinary Calculi

In 3,000 calculi, monosodium urate was detected in 50 cases (1.66%). Infrared frequencies of monosodium urate are reported. In thin sections it appeared as long and thin fan-shaped or feather-like arranged crystals. Six calculi had monosodium urate as the sole component but all other cases were of mixed composition, with whewellite as the main secondary substance. The relative scarcity of monosodium urate cannot be explained by its high aqueous solubility because in urine the solubility decreases with increasing sodium concentration. Monosodium urate should be suspected in radiolucent calculi with neutral or light alkaline reaction and high uric acid and sodium concentrations in the patient’s urine.Peer reviewe