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Kidney stones (renal calculi)
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.