Urates in uric acid renal calculi

Area of Science:

• Nephrology
• Urology
• Materials Science

Background:

• Uric acid calculi are common urinary stones.
• The precise composition of uric acid calculi is not fully understood.
• Investigating impurities in uric acid stones is crucial for understanding stone formation and developing treatments.

Purpose of the Study:

• To determine the presence and types of impurities, specifically calcium urate, sodium, potassium, and calcium, within calculi described as 'pure' uric acid stones.
• To characterize the composition of these urinary calculi beyond just uric acid.

Main Methods:

• Examination of ten spontaneously passed uric acid urinary calculi.
• Utilized stereoscopic microscopy, infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray analysis for detailed compositional analysis.

Main Results:

• Two out of ten calculi were found to be near-pure calcium urate.
• All analyzed uric acid calculi contained calcium-enriched urate zones.
• Complex urates, with varying proportions of sodium, potassium, and calcium, were observed on the surface, with potassium often predominant. Ammonium urate was notably absent.

Conclusions:

• The study demonstrates that urinary uric acid calculi are frequently impure.
• The presence of 'complex urates' involving sodium, potassium, and calcium in diverse ratios is common in uric acid stones.
• These findings challenge the notion of 'pure' uric acid calculi and highlight the complexity of urinary stone composition.