What are the two most common types of kidney stones and their primary risk factors?

• A. Calcium Oxalate Stones with Hypercalciuria, Low Urine Volume, High Oxalate Intake; Calcium Phosphate Stones with Alkaline Urine and High Calcium
• B. Calcium Oxalate Stones and Uric Acid Stones
• C. Struvite Stones and Cystine Stones
• D. Uric Acid Stones and Calcium Phosphate Stones

Answer: (A)

Calcium-based stones are by far the most common type of kidney stones, and the two most frequent forms are calcium oxalate stones and calcium phosphate stones. Calcium oxalate stones form when calcium in the urine binds with oxalate. The main risk factors that promote this form are hypercalciuria (high calcium in the urine), low urine volume (which concentrates stone-forming substances), and high oxalate intake (more oxalate available to bind with calcium).

Calcium phosphate stones form in urine that is more alkaline (higher pH) and can also be promoted by high urinary calcium. So, the combination of alkaline urine and calcium presence favors calcium phosphate stone formation.

Other stone types exist—uric acid stones, struvite stones, and cystine stones—but they are less common overall, and they are associated with different conditions (low urine pH for uric acid, infection for struvite, genetic transport defects for cystine), not the general risk pattern described for the two most common calcium-based stones.