Kidney Stones (Nephrolithiasis)

Kidney stones (nephrolithiasis) are hard mineral and salt deposits that form inside the kidneys when there is not enough fluid in the urine to keep minerals dissolved. They can be as small as a grain of sand or, rarely, as large as a golf ball — though most are much smaller. Small stones often pass on their own; larger stones may need procedures to break them up or remove them. Kidney stones affect roughly 1 in 10 people over a lifetime and have a high recurrence rate without preventive measures.

Types of kidney stones

Calcium oxalate stones — the most common type, accounting for around 80% of cases. They form when calcium combines with oxalate in the urine, often in people with low fluid intake, high sodium diets, or certain metabolic conditions. You do not usually need to avoid high-oxalate foods entirely, but pairing them with dietary calcium and staying well hydrated can reduce risk.

Calcium phosphate stones — less common. Often associated with renal tubular acidosis (a condition where the kidneys cannot properly regulate acid) or hyperparathyroidism (overactive parathyroid glands that raise calcium levels).

Uric acid stones — form when urine is persistently acidic. Associated with gout, high-purine diets (red meat, shellfish), obesity, and diabetes.

Struvite stones — form in response to urinary tract infections caused by certain bacteria that split urea and make the urine more alkaline. Can grow rapidly and become large.

Cystine stones — rare, caused by a genetic disorder (cystinuria) that leads to excess cystine in the urine. Often presents in childhood or young adulthood.

Symptoms

Symptoms depend on the size and location of the stone. Many small stones cause no symptoms and pass unnoticed. When a stone moves into the ureter and blocks urine flow, symptoms typically include:

• Severe, sharp pain in the side and back, below the ribs (renal colic) that radiates to the lower abdomen and groin
• Pain that comes in waves and fluctuates in intensity
• Burning or pain during urination
• Pink, red, or brown urine (haematuria)
• Cloudy or foul-smelling urine
• Nausea and vomiting
• Persistent urge to urinate or increased frequency

Seek urgent medical evaluation if you have:

• Fever and chills alongside stone symptoms — this can signal a serious infection requiring immediate treatment
• Pain so severe you cannot get comfortable
• Inability to keep fluids down due to vomiting

Causes and risk factors

Kidney stones form when urine contains more crystal-forming substances than available fluid can dilute. Staying well hydrated is the single most important preventive step for most people.

• Low fluid intake — the most modifiable risk factor; concentrated urine strongly promotes crystal formation
• High-sodium diet — increases calcium excretion in urine
• High animal protein diet — raises uric acid and reduces citrate, a natural stone inhibitor
• High-oxalate foods without adequate calcium — spinach, nuts, chocolate, and tea in high amounts can raise risk in predisposed individuals
• Obesity — alters urinary pH and increases stone-forming substances
• Family history — having a close relative with kidney stones roughly doubles your lifetime risk
• Hyperparathyroidism — raises blood and urine calcium levels
• Gout — associated with uric acid stone formation
• Inflammatory bowel disease or malabsorption — increases intestinal oxalate absorption
• Recurrent urinary tract infections — risk factor specifically for struvite stones
• Certain medications — including some diuretics, calcium-based antacids, and antiretrovirals; always discuss with your healthcare provider before changing any prescribed medicine

Diagnosis

• CT scan (non-contrast) — the most sensitive imaging test; detects almost all stone types and sizes. Low-dose CT is often used to limit radiation exposure
• Ultrasound — preferred in pregnancy and for follow-up, as it uses sound waves instead of radiation; less sensitive for small stones
• Urinalysis — may show red blood cells, white blood cells, crystals typical of certain stone types, and changes in urine pH
• 24-hour urine collection — measures calcium, oxalate, uric acid, citrate, and creatinine; often performed after a stone event in people at higher risk of recurrence to identify metabolic causes
• Blood tests — assess calcium, uric acid, creatinine, and parathyroid hormone
• Stone analysis — if a stone is passed or retrieved, chemical analysis of its composition guides targeted prevention

Treatment

Watchful waiting (stones smaller than about 5–6mm) Most small stones pass spontaneously within 2–6 weeks with adequate hydration (2–3 litres of fluid daily, unless your doctor has advised a fluid restriction for another reason). Alpha-blockers such as tamsulosin may help relax the ureter and facilitate passage. NSAIDs such as ibuprofen or diclofenac are usually first-line for pain unless contraindicated.

Procedures for larger or obstructing stones

• Shockwave lithotripsy (SWL) — external sound waves break stones into fragments that pass in urine; most effective for stones under 2cm
• Ureteroscopy — a thin scope passed through the urethra and bladder allows laser fragmentation or direct stone removal
• Percutaneous nephrolithotomy (PCNL) — surgical removal through a small back incision; used for large or complex stones

Prevention

Lifestyle changes (recommended for all stone formers)

• Increase fluid intake to produce at least 2–2.5 litres of urine daily
• Reduce sodium and animal protein intake
• Maintain a healthy weight
• Pair calcium-rich foods with oxalate-rich foods rather than avoiding either completely

Medications for recurrent stones (usually prescribed after metabolic evaluation)

• Thiazide diuretics — reduce urinary calcium excretion in recurrent calcium stone formers
• Potassium citrate — raises urinary citrate and pH, reducing calcium oxalate and uric acid stone formation
• Allopurinol — reduces uric acid production in uric acid stone formers

Working with a dietitian or clinician before making major dietary changes is advisable, particularly for people with recurrent stones or underlying metabolic conditions.

Related biomarkers

Several lab markers are relevant to kidney stone diagnosis and monitoring, including urine pH, urine and serum calcium, urine and serum uric acid, oxalate, citrate, creatinine, and white blood cells in urine. Patterns in these markers can help identify why stones are forming — for example, high urine calcium or low citrate — and whether preventive treatments are working over time. Tracking results in HealthMatters makes it easier to spot trends across multiple tests.