What are kidney stones?

Kidney stones are hard deposits of minerals and salts that form inside the kidneys. They develop when substances in urine — like calcium, oxalate, and uric acid — become too concentrated and crystallize. Over time, these crystals grow into stones that range in size from a grain of sand to a golf ball.

Small stones often pass on their own through the urinary tract without causing many problems. Larger stones can get stuck and cause intense pain, blockage, and infection.

About 1 in 10 people will develop a kidney stone at some point in their life. Once you've had one, the chance of getting another within 10 years is about 50% — which is why prevention matters.

Types of kidney stones

Calcium oxalate stones (most common — ~80%) — Form when calcium and oxalate combine in urine. Risk factors include dehydration, high-oxalate diet, and certain medical conditions.
Uric acid stones (~10%) — Form when urine is too acidic. Common in people with gout, diabetes, or who eat very high-protein diets.
Struvite stones — Form after recurrent urinary tract infections. Can grow very large quickly.
Cystine stones — Rare, caused by a genetic disorder (cystinuria) that causes the kidneys to leak too much of the amino acid cystine.

Symptoms

When a stone moves from the kidney into the ureter (the tube connecting kidney to bladder), it causes:

  • Sudden, severe pain in the back or side — often described as the worst pain imaginable, worse than childbirth or surgery
  • Pain that radiates to the lower abdomen and groin as the stone moves
  • Pain that comes in waves and fluctuates in intensity
  • Blood in the urine (pink, red, or brown)
  • Nausea and vomiting from the intense pain
  • Frequent, painful urination when the stone reaches the bladder
  • Fever and chills if infection is present — seek emergency care immediately

Treatment

For small stones (usually less than 5mm)

Most small stones pass on their own within a few days to a few weeks. Treatment focuses on managing pain (NSAIDs or stronger medications) and staying well hydrated (2–3 liters of water per day to help flush the stone). Your doctor may prescribe a medication called an alpha-blocker (tamsulosin) that relaxes the ureter and helps the stone pass faster.

For larger stones or stones that won't pass

  • Shock wave lithotripsy (SWL) — Sound waves from outside the body break the stone into smaller pieces that can then pass in urine. Non-invasive, done as an outpatient procedure.
  • Ureteroscopy — A thin scope is passed up through the urethra and bladder to the stone, which is then broken up with a laser or removed. Most common procedure for stones in the ureter or kidney.
  • Percutaneous nephrolithotomy (PCNL) — For very large stones. A small incision in the back allows direct removal of the stone. Done under general anesthesia.

Prevention — the most important part

Once you've had a kidney stone, preventing the next one is critical. What works depends on the type of stone — which is why analyzing the stone (if you can catch it) and doing a 24-hour urine collection is so valuable.

Drink more water — The single most effective prevention. Aim for 2.5–3 liters of fluid per day. Your urine should be pale yellow, not dark.
Reduce sodium — High salt intake increases calcium in urine. Limit to 2,300mg sodium per day.
Don't avoid calcium — Counterintuitively, eating normal amounts of dietary calcium (from food, not supplements) actually reduces calcium oxalate stone risk by binding oxalate in the gut.
Limit high-oxalate foods — Spinach, rhubarb, almonds, and chocolate if you form calcium oxalate stones.
Limit animal protein — Red meat, poultry, and shellfish increase uric acid and can promote stone formation.
If you pass a stone, try to collect it in a strainer and bring it to your doctor. Stone analysis tells us exactly what type it is, which guides the most effective prevention strategy.