Kidney stones are common. They can form anywhere in the urinary tract, but usually in the kidney. Stone constituents become concentrated in the urine due to increased excretion or reduced urine volume, and begin to crystallize and grow. 80% of all stones contain calcium (as oxalate, sometimes as phosphate). Struvite stones, containing calcium, ammonia and phosphate, can form in presence of urine infections. Uric acid stones form from the substance which causes gout. Cystine stones occur in the inherited condition cystinuria and are rare. Occasionally some drugs can form crystals and stones.
- Severe loin pain, travelling anteriorly and into testis/ labium, sometimes in colicky waves
- With complications – urinary tract obstruction or infection
- Male sex (3 times as likely as females)
- Age 30-60 years
- Hot climate
- Caucasian race
- Family history of stones
- Abnormal urinary tract – infection, scars or cysts
- Low urine flow (hot climates, low fluid intake)
- High urinary calcium, oxalate, urate – genetic, dietary, etc
- Inherited disorders (e.g. medullary sponge kidney, cystinuria, renal tubular acidosis)
- Urinary tract obstruction/infection
- Analgesia – opiates often required
- Hydration to ensure adequate urine flow
- Investigation – Stones may be visible on plain X-ray but intravenous urography (IVU) or (better) CT scanning will show both stones and obstruction.
- Stones of <4mm usually pass spontaneously. Stones >6mm usually require intervention.
- Lithotripsy and percutaneous techniques have revolutionised management of larger stones and of obstruction.
- For recurrent stones, test stone for composition, measure 24h urinary excretion of sodium, calcium, oxalate, urate. Blood for calcium, renal function, urate.
General measures for recurrent calcium stones
- Increase fluid intake as much as possible, particularly at night.
- Moderate (not high) protein intake
- Low salt intake
- Increase dietary calcium (binds oxalate in gut) but avoid calcium supplements (dietetic advice valuable)
- Thiazide diuretics reduce urine calcium