Kidney Stones

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A kidney stone is a hard mass of crystallized minerals and salts that forms inside the kidney when urine becomes too concentrated. Stones vary widely in size — from a tiny grain of sand to a stone that fills the entire kidney — and their composition also differs, with calcium oxalate being the most common type, followed by uric acid, struvite and cystine stones.

Small stones often pass unnoticed. Larger stones, or ones that move into the ureter (the tube connecting the kidney to the bladder), can cause sudden, severe pain and may block the normal flow of urine, which is when most people first seek medical attention.

Kidney stones form when urine contains more crystal-forming substances — calcium, oxalate, uric acid — than the fluid in the urine can dilute. At the same time, urine may lack the substances that normally prevent crystals from sticking together, allowing a stone to gradually form.

Diagnosis typically starts with a urine test to check for blood, crystals or signs of infection, and a blood test to assess kidney function and mineral levels. Imaging confirms the stone's size and exact location — an ultrasound is often the first step, while a non-contrast CT scan of the kidneys, ureters and bladder (CT KUB) offers the most detailed picture and is considered the gold standard for treatment planning.

The single most effective preventive step is staying well hydrated throughout the day, aiming for urine that stays consistently pale in color. Moderating salt and animal protein intake, maintaining a healthy weight, and — for anyone who has already had more than one stone — asking about a metabolic evaluation to identify specific dietary triggers, all meaningfully reduce the chance of forming another stone.

Spreading fluid intake evenly across the day, rather than drinking a large amount at once, keeps urine consistently dilute. Reducing processed and salty foods, moderating red meat portions, and including citrus fruits (a natural source of citrate, which helps prevent crystal formation) are all practical, sustainable habits for anyone prone to stones.