Kidney stones are solid masses made of minerals and salts found in urine. They develop inside the kidneys and are sometimes referred to as renal calculi, nephrolithiasis, or urolithiasis.
There are many possible causes of kidney stones, including diet, excess body weight, certain medical conditions, and the use of specific supplements and medications. Kidney stones can affect any part of the urinary system, from the kidneys to the bladder. Often, they form when urine contains too little water, allowing minerals to crystallize and clump together.
Passing a kidney stone can be extremely painful, but timely treatment typically prevents long-term complications. In some cases, simply drinking a large amount of water and taking pain relief is enough to pass a stone. In other cases, surgery or other interventions may be required, depending on the stone’s size, type, and location.
If you’ve had more than one kidney stone, a urologist can help you reduce your risk of developing more through dietary changes, medication, or both.
Symptoms
A kidney stone typically does not cause symptoms until it moves within the kidney or enters one of the ureters, which are the tubes that connect the kidneys to the bladder.
When a stone becomes lodged in a ureter, it can block urine flow, causing the kidney to swell and the ureter to spasm. This results in intense pain. Symptoms may include:
- Severe, sharp pain in the side and back, below the ribs
- Pain radiating to the lower abdomen and groin
- Pain that fluctuates in intensity and comes in waves
- Pain or burning sensation during urination
Other signs may include:
- Urine that appears pink, red, or brown
- Cloudy or foul-smelling urine
- A persistent urge to urinate, urinating more frequently, or in small amounts
- Nausea and vomiting
- Fever and chills, especially if there’s an infection
Pain may shift or intensify as the stone moves through the urinary tract.
When to see a urologist
Seek medical attention from a urologist if you experience any concerning symptoms. Immediate care is needed if you have:
- Pain so intense that sitting still or finding a comfortable position is impossible
- Pain with nausea and vomiting
- Pain with fever and chills
- Blood in the urine
- Difficulty urinating
Causes
There is often no single, definite cause of kidney stones, but various factors may increase the risk.
Kidney stones form when urine contains more crystal-forming substances – such as calcium oxalate, calcium phosphate, and uric acid – than the fluid in the urine can dilute. A lack of substances that prevent crystals from sticking together also creates an ideal environment for stone formation.
Types of Kidney Stones
Identifying the type of stone helps the urologist determine the cause and appropriate treatment. It also guides prevention strategies. If possible, save a stone you pass and bring it to your urologist for analysis.
Types include:
- Calcium stones: These are the most common and typically consist of calcium oxalate. Oxalate is naturally produced by the liver and absorbed from certain foods like nuts, chocolate, and some fruits and vegetables. Conditions such as intestinal bypass surgery and high vitamin D intake can increase calcium or oxalate in the urine.
Calcium phosphate stones are linked to metabolic conditions like renal tubular acidosis and may be associated with medications like topiramate used for migraines or seizures. - Uric acid stones: These occur in people who lose too much fluid from chronic diarrhoea, consume high-protein diets, or have diabetes or metabolic syndrome. Genetics may also play a role.
- Struvite stones: These form in response to urinary tract infections. They can grow rapidly and become quite large with minimal symptoms.
- Cystine stones: These result from a rare inherited disorder called cystinuria, where the kidneys excrete excessive cystine.
Risk Factors
Risk factors for kidney stones include:
- Family or personal history: If kidney stones run in your family or you’ve had them before, your risk increases.
- Dehydration: Inadequate water intake can lead to concentrated urine, raising the risk of stone formation. People living in hot, dry climates or who sweat heavily may be more susceptible.
- Certain diets: High intake of oxalates, protein, salt, and sugar increases risk. A sodium-rich diet especially raises urinary calcium levels.
- Obesity: Being overweight is linked with increased kidney stone risk.
- Digestive conditions and surgeries: Procedures like gastric bypass, inflammatory bowel disease, or chronic diarrhoea can affect nutrient absorption, increasing urinary stone-forming substances.
- Other medical conditions: These include renal tubular acidosis, cystinuria, hyperparathyroidism, and recurrent urinary tract infections. A rare genetic condition, primary hyperoxaluria, also increases the risk.
- Supplements and medications: These include vitamin C, excessive laxative use, calcium-based antacids, and certain drugs used to treat migraines and depression.
Prevention
Kidney stone prevention often combines lifestyle modifications and medication.
Lifestyle changes
You can reduce your risk by:
- Drinking water consistently throughout the day: Aim for enough fluid intake to produce at least 2 litres of urine per day. If you exercise often or live in a warm climate, you may need more. Clear or pale urine is a good sign of adequate hydration.
- Reducing oxalate-rich foods: If you are prone to calcium oxalate stones, avoid or limit foods such as rhubarb, spinach, beets, okra, nuts, chocolate, tea, black pepper, soy, sesame, and tahini.
- Eating less sodium and animal protein: Use plant-based proteins like legumes and consider salt alternatives.
- Consuming calcium-rich foods with care: Dietary calcium does not usually raise kidney stone risk, but calcium supplements might. Always take supplements with food and only under your urologist’s advice.
- Consulting a dietitian: A specialist can tailor a diet plan to help prevent stones.
Medications
Drugs can adjust the mineral and salt balance in your urine, depending on the type of stone:
- Calcium stones: May be treated with thiazide diuretics or potassium citrate. For primary hyperoxaluria, vitamin B6 or specific drugs like lumasiran or nedosiran may be used.
- Uric acid stones: May be treated with allopurinol and potassium citrate, which may also dissolve existing stones.
- Struvite stones: Prevention focuses on managing infections. This might include drinking fluids, urinating frequently, and occasionally using antibiotics or acetohydroxamic acid.
- Cystine stones: A low-sodium, low-protein diet and high fluid intake may help. If not enough, thiol-based drugs or newer medications may be used.
Diagnosis
Diagnosis starts with a physical examination and may include:
- Blood tests: To assess levels of calcium, uric acid, and kidney function.
- Urine testing: You may be asked to collect urine over 24 hours to analyse mineral levels and stone-preventing substances.
- Imaging: CT scans, especially dual-energy types, can detect even tiny stones. X-rays are used less due to their limited sensitivity. Ultrasound is another effective option.
- Stone analysis: If you pass a stone, straining your urine can help collect it for chemical analysis.
- Genetic testing: Rare inherited conditions like cystinuria or primary hyperoxaluria may be identified through genetic screening.
Treatment
Treatment varies depending on the type and cause of the stone.
Small stones with minimal symptoms
These usually pass on their own with:
- Hydration: Drinking 1.8 to 3.6 litres of fluid per day can help flush out stones.
- Pain relief: Mild to moderate pain can be managed with ibuprofen or naproxen sodium. Severe pain may require stronger medications.
- Alpha blockers: These relax ureter muscles, helping stones pass more easily. Examples include tamsulosin or dutasteride-tamsulosin.
Large stones or those causing complications
More extensive treatments include:
- Extracorporeal Shock Wave Lithotripsy (ESWL): Uses sound waves to break stones into smaller fragments that pass through urine. The procedure lasts about 45–60 minutes and may cause moderate pain or bruising.
- Percutaneous nephrolithotomy: A surgical procedure to remove large stones using small instruments inserted through a small incision in the back. General anaesthesia is used, and a short hospital stay is typically required.
- Ureteroscopy: Involves inserting a scope through the urethra to locate and remove or break up smaller stones. A stent may be placed afterward to aid healing.
- Parathyroid surgery: For stones caused by overactive parathyroid glands, surgery may be needed to remove benign tumours or treat underlying conditions causing excess hormone production.