[Blog](https://vittalkamath.com/blog) # Kidney stones (renal calculi) 11 May 2026 Kidney stones are hard, pebble-like deposits of minerals and salts — most commonly calcium oxalate — that form inside the kidneys when urine becomes too concentrated. ## Symptoms Small stones may pass unnoticed. With bigger stones: - **Pain:** usually flank pain that starts suddenly and comes in waves. It often starts in the back or side, below the ribs, and radiates to the lower abdomen or groin. - **Urinary changes:** foul-smelling urine is more typical of an infection. For stones alone: cloudy urine, blood (pink, red or brown urine), urgency. ## Causes and risk factors - **Dehydration:** the number one risk you can change. The goal is more than 2.5 L of urine a day, which usually means about 2–3 L of water. - **Diet:** high sodium increases calcium in the urine. High animal protein raises uric acid and lowers citrate. - **Medicines:** topiramate and protease inhibitors can also cause stones. ## Kinds of stone Stone Key driver Share of stones Calcium oxalate Low urine volume, high oxalate, low citrate ~80% Calcium phosphate Alkaline urine, hyperparathyroidism ~10% Uric acid Acidic urine, high-protein diet, gout ~5–10% Struvite Urinary infections with urease-producing bacteria ~5–10% Cystine Genetic cystinuria ~1% ## Prevention - **Citrate:** lemon or lime juice helps raise urinary citrate, which blocks stone formation. - **The calcium paradox:** calcium in the diet — rather than calcium supplements — binds oxalate in the gut and lowers the risk. - **Oxalates:** don’t cut out all oxalates unless you are known to excrete a lot of them. Pair high-oxalate foods with calcium-rich foods. ## Diagnosis and treatment - **CT scan:** a non-contrast CT is the gold standard for diagnosis. - **Alpha blockers:** tamsulosin can help stones of 5–10 mm pass, especially in the lower ureter. - **When to go to hospital:** fever with stone pain, vomiting that won’t stop, a single kidney with a blockage, or severe pain not controlled by medicines. [All articles](https://vittalkamath.com/blog)