Kidney Stones

Overview

Kidney stones are hard deposits of minerals and salts that form inside the kidneys. They develop when urine becomes concentrated, allowing minerals to crystallize and bind together. Stones can form anywhere in the urinary tract—from the kidneys through the ureters to the bladder—and range in size from a grain of sand to a golf ball.

Approximately 10% of people will develop a kidney stone during their lifetime, with men affected more often than women. The condition tends to recur: about half of people who pass one stone will develop another within ten years without preventive measures. Most small stones pass on their own with increased fluid intake and pain management, but larger stones may require surgical intervention.

Types

Calcium stones account for about 80% of all kidney stones. Most are calcium oxalate, though some contain calcium phosphate. These stones form when urine contains excess calcium, oxalate, or both, often related to diet, dehydration, or metabolic abnormalities.

Uric acid stones make up 5-10% of cases and develop when urine becomes too acidic. People with gout, those who eat high-protein diets, and individuals with diabetes or obesity face increased risk. Unlike calcium stones, uric acid stones can sometimes dissolve with medication that alkalinizes the urine.

Struvite stones (5-10%) form in response to urinary tract infections. Bacteria that produce urease enzyme break down urea, raising urine pH and promoting struvite crystal formation. These infection stones can grow rapidly into large “staghorn” calculi that fill the kidney’s collecting system. Women develop struvite stones more often than men due to higher UTI rates.

Cystine stones (1-2%) result from cystinuria, a genetic disorder causing excessive cystine excretion in urine. These stones tend to recur frequently and require lifelong management with very high fluid intake and medications.

Symptoms

The classic symptom of kidney stones is renal colic—sudden, severe pain that begins in the flank below the ribs and radiates around the abdomen to the groin. This pain comes in waves as the ureter spasms around the stone, often described as among the worst pain a person can experience. Patients with renal colic typically cannot find a comfortable position and may pace or writhe in distress.

Pain location provides clues about stone position. Stones in the kidney may cause a dull ache or remain asymptomatic. When a stone enters the ureter, the pain becomes sharp and colicky. Stones near the bladder often cause frequent urination and urgency. Other common symptoms include blood in the urine (appearing pink, red, or brown), nausea and vomiting, painful urination, and cloudy or foul-smelling urine. Fever and chills indicate infection, which requires urgent evaluation.

Causes

Dehydration stands as the most important modifiable risk factor for kidney stones. When fluid intake is inadequate, urine becomes concentrated with stone-forming minerals. People living in hot climates, those with physically demanding jobs, and individuals who simply don’t drink enough water face elevated risk.

Dietary factors play a significant role. High sodium intake increases urinary calcium excretion, promoting calcium stone formation. Excessive animal protein raises uric acid levels and lowers urinary citrate, a natural stone inhibitor. Paradoxically, dietary calcium actually protects against stones by binding oxalate in the gut, while calcium supplements taken between meals may increase risk.

Medical conditions associated with kidney stones include gout, hyperparathyroidism, type 2 diabetes, inflammatory bowel disease, and chronic diarrhea. Gastric bypass surgery increases stone risk by altering oxalate absorption. Recurrent urinary tract infections predispose to struvite stone formation. Family history of stones doubles an individual’s risk, reflecting both genetic and shared environmental factors.

Certain medications can promote stone formation, including high-dose vitamin C supplements, some diuretics, certain HIV medications, and antibiotics like ciprofloxacin and sulfonamides.

Diagnosis

Non-contrast computed tomography (CT) is the gold standard for diagnosing kidney stones, revealing stone size, location, and density with high accuracy. Ultrasound avoids radiation exposure and works well for follow-up imaging, though it may miss small ureteral stones. Plain abdominal X-ray can visualize calcium-containing stones but fails to detect uric acid and cystine stones, which are radiolucent.

Laboratory evaluation includes urinalysis to check for blood, infection, and crystals, plus blood tests measuring kidney function, calcium, and uric acid levels. When a stone is passed or surgically removed, laboratory analysis identifies its composition to guide prevention strategies.

For patients with recurrent stones, a 24-hour urine collection provides essential information about stone risk factors. This comprehensive metabolic evaluation measures urine volume, pH, calcium, oxalate, citrate, uric acid, sodium, and other parameters to identify specific abnormalities driving stone formation.

Treatment

Most stones smaller than 5mm pass spontaneously with conservative management. Treatment focuses on hydration (2-3 liters daily to flush the urinary tract), pain control with nonsteroidal anti-inflammatory drugs or opioids for severe pain, and anti-nausea medication. Medical expulsive therapy with tamsulosin (an alpha-blocker) relaxes ureteral smooth muscle and improves stone passage rates.

Intervention becomes necessary when stones exceed 10mm, cause uncontrollable pain, obstruct the kidney with concurrent infection (a urologic emergency), impair kidney function, or fail to pass after 4-6 weeks of observation.

Shock wave lithotripsy (ESWL) uses externally generated shock waves to fragment stones into passable pieces. This noninvasive outpatient procedure works best for kidney stones under 2cm and stones in the upper ureter, though hard stones and those in the lower ureter respond less favorably.

Ureteroscopy involves passing a thin scope through the urethra and bladder into the ureter. Laser energy breaks the stone into fragments, which are then removed. This approach achieves excellent results for ureteral stones and can treat kidney stones up to moderate size.

Percutaneous nephrolithotomy (PCNL) addresses large kidney stones exceeding 2cm. Through a small incision in the back, surgeons insert a nephroscope directly into the kidney to fragment and remove the stone. PCNL provides the most effective treatment for large or complex stones, including staghorn calculi.

Prevention

General measures benefit all stone formers. Drinking enough fluid to produce at least 2 liters of urine daily dilutes stone-forming substances. Limiting sodium intake to under 2,300mg daily reduces urinary calcium. Moderate animal protein consumption (rather than excessive meat intake) helps maintain favorable urine chemistry. Maintaining healthy weight and staying physically active further reduce risk.

For calcium stone formers, eating adequate dietary calcium (from food, not supplements) paradoxically protects against stones by binding intestinal oxalate. Limiting high-oxalate foods such as spinach, rhubarb, nuts, and chocolate may help in susceptible individuals. Increasing citrus fruit consumption provides citrate, a natural stone inhibitor. Medications including thiazide diuretics (which reduce urinary calcium) and potassium citrate (which raises urine citrate and pH) offer additional prevention for recurrent stone formers.

Uric acid stone prevention centers on reducing purine-rich foods like organ meats and shellfish, moderating overall animal protein, and alkalinizing the urine with potassium citrate. Allopurinol may be added for patients with elevated uric acid levels.

Struvite stone prevention requires aggressive treatment of urinary tract infections and complete surgical removal of all stone material to prevent regrowth. Long-term suppressive antibiotics may be necessary for patients with recurrent UTIs.

Cystine stone prevention demands very high fluid intake (over 3 liters daily) to keep cystine soluble, urine alkalinization, and medications such as tiopronin or D-penicillamine that increase cystine solubility.

When to See a Doctor

Seek urgent evaluation for any episode of severe flank pain, especially if accompanied by blood in the urine, nausea, or vomiting. Emergency care is essential if you develop fever with kidney stone symptoms (indicating possible infected hydronephrosis), become unable to urinate, experience persistent uncontrollable pain despite medication, or notice blood clots in the urine.

After passing a stone, follow up with a urologist for metabolic evaluation to identify the cause and develop a prevention strategy. Catch passed stones by urinating through a strainer—stone analysis guides targeted prevention. Patients who have had one stone should adopt preventive measures, as the recurrence rate without intervention approaches 50% within a decade. Regular follow-up imaging monitors for new stone formation, and those with identified metabolic abnormalities benefit from ongoing medication management and periodic 24-hour urine testing to ensure treatment effectiveness.