Which is the most common composition of kidney stones?

• A. Calcium oxalate
• B. Uric acid
• C. Struvite
• D. Calcium phosphate

Answer: (A)

Calcium oxalate stones are the most common type of kidney stone, accounting for the majority of cases. They form when calcium binds with oxalate in the urine, and this can happen when there’s either excess calcium or oxalate excretion, low urine volume, or dietary factors that raise oxalate intake or calcium binding in the gut. Because calcium and oxalate are common in many foods and are readily absorbed, this combination appears most frequently in stone formation.

In contrast, uric acid stones arise from acidic urine and high uric acid levels; struvite stones develop with chronic infection by urease-producing bacteria; and calcium phosphate stones are more tied to high urine pH or certain metabolic conditions. Calcium-containing stones are typically radiopaque on plain X-ray, reflecting their calcium content. Prevention emphasizes higher fluid intake, moderating dietary oxalate, ensuring adequate dietary calcium to help bind oxalate in the gut, and addressing any process that increases urinary calcium or oxalate excretion.