Kidney Stone Types

A kidney stone forms when urine becomes supersaturated with a substance that can crystallize. Crystals enlarge, aggregate, and may lodge in the ureter, producing obstruction and the sudden, wave-like pain of renal colic. The composition matters because the urine chemistry that created one stone may not create another. Calcium oxalate stones, including monohydrate and dihydrate forms, are the most prevalent type in Canada. Hypercalciuria, increased oxalate absorption or excretion, low urinary citrate, and acidic urine all increase risk. Dietary calcium is not automatically the enemy: calcium eaten with meals binds oxalate in the intestine and can reduce oxalate absorption. Excess sodium, however, promotes urinary calcium loss. Uric acid stones form when urine remains persistently acidic, usually below pH 5.5. Hyperuricemia, gout, and a high-purine diet increase the available uric acid, but low urine pH is the factor that keeps it poorly soluble. Pure uric acid stones may be missed on a plain radiograph, whereas non-contrast CT can detect them. Struvite stones are magnesium-ammonium-phosphate infection stones. Urease-producing organisms split urea and make the urine alkaline, allowing the stone to grow rapidly....