Routine analysis of urinary calculi by scanning electron microscopy

Area of Science:

• Nephrology
• Biochemistry
• Materials Science

Background:

• Urinary calculi (kidney stones) are a significant health issue.
• Current theories on stone formation, such as the primary nidus theory and the matrix theory, are often considered contradictory.
• Understanding the initial steps of stone formation is crucial for developing effective prevention and treatment strategies.

Purpose of the Study:

• To investigate the composition and structure of urinary calculi.
• To identify the initial components involved in kidney stone formation.
• To propose a unified model for urinary stone genesis.

Main Methods:

• Analysis of 529 urinary calculi using Scanning Electron Microscopy with Energy Dispersive X-ray Analysis (SEM/EDXA).
• X-ray diffraction was employed to determine the mineralogical composition of the stones.
• Characterization of calcium phosphate-rich microspherules in calculi, urine, and kidney tissue.

Main Results:

• Oxalate-rich stones consistently contained calcium phosphate, often in the central core (in over 75% of cases).
• Calcium phosphate-bearing microspherules were abundant in urinary calculi and urine of stone formers.
• Similar microspherules were identified in human kidney tissue, suggesting a common origin.
• The findings support the existence of a primary nidus in stone formation.

Conclusions:

• Calcium phosphate plays a critical role as a primary nidus in the formation of urinary calculi, including oxalate-rich stones.
• The presence of calcium phosphate microspherules provides insight into the physico-chemical nature of the initial stone-forming aggregate.
• A novel model is proposed that integrates previously disparate theories of urinary stone genesis.