Kidney Stones

Overview

Kidney stones form when urine contains more crystal-forming substances—such as calcium, oxalate, and uric acid—than the fluid in urine can dilute. Simultaneously, urine may lack substances that prevent crystals from sticking together, creating an ideal environment for kidney stone formation. The process begins with supersaturation of urine with stone-forming salts, followed by crystal nucleation, growth, and aggregation. These stones can develop in one or both kidneys and can travel down the ureters, into the bladder, and out through the urethra.

There are several types of kidney stones, each with different compositions and causes. Calcium stones, primarily calcium oxalate, account for about 80% of all kidney stones. Struvite stones (10-15%) form in response to urinary tract infections. Uric acid stones (5-10%) develop in people who lose too much fluid, eat high-protein diets, or have gout. Cystine stones (<1%) form in people with a hereditary disorder causing the kidneys to excrete excessive amounts of certain amino acids. Understanding the stone type is crucial for determining appropriate treatment and prevention strategies.

The incidence of kidney stones has been rising globally, attributed to dietary changes, increasing obesity rates, and climate change leading to dehydration. Men are affected more frequently than women, with a lifetime risk of 19% for men and 9% for women. The peak age of onset is between 30 and 50 years, though stones can occur at any age. Geographic location also plays a role, with higher rates in warmer climates—the so-called "stone belt" in the southeastern United States. Without preventive measures, approximately 50% of people who have had one kidney stone will develop another within 5-10 years.

Symptoms

Kidney stone symptoms can vary dramatically depending on the size, location, and whether the stone is moving. Small stones may cause no symptoms and pass unnoticed, while larger stones or those causing obstruction can produce severe symptoms that require emergency treatment.

Primary Symptoms

• Side pain (flank pain) - severe, sharp pain below the ribs
  • Often described as the worst pain ever experienced
  • Comes in waves and fluctuates in intensity
  • May radiate to lower abdomen and groin
  • Changes in intensity as stone moves
• Back pain and low back pain
  • May be constant or intermittent
  • Worsens with movement
  • Different from typical muscle strain
• Sharp abdominal pain and lower abdominal pain
  • Pain location changes as stone moves
  • May mimic other abdominal conditions
  • Often accompanied by restlessness

Urinary Symptoms

• Blood in urine (hematuria)
  • May be visible (gross hematuria) or microscopic
  • Urine may appear pink, red, or brown
  • Often the first sign of kidney stones
• Painful urination (dysuria)
  • Burning sensation during urination
  • More pronounced when stone nears bladder
  • May persist after stone passage
• Frequent urination
  • Urgent need to urinate
  • Small amounts of urine produced
  • Sensation of incomplete emptying
• Retention of urine
  • Complete blockage preventing urination
  • Medical emergency requiring immediate treatment
  • May cause kidney damage if prolonged

Associated Symptoms

• Vomiting and nausea
  • Common response to severe pain
  • May lead to dehydration
  • Can complicate stone passage
• Suprapubic pain - pain above the pubic bone
• Fever and chills - indicates possible infection
• Cloudy or foul-smelling urine
• Restlessness and inability to find comfortable position
• Sweating and pale skin from pain

Location-Specific Symptoms

• Kidney (renal pelvis): Dull, constant flank pain
• Upper ureter: Severe flank pain radiating to abdomen
• Mid-ureter: Pain radiating to lateral abdomen
• Lower ureter: Pain radiating to groin, testicles, or labia
• Bladder: Suprapubic pain, urgency, frequency

Warning Signs Requiring Emergency Care

• Fever above 101.5°F (38.6°C) with pain
• Severe pain uncontrolled by medication
• Persistent vomiting preventing fluid intake
• Complete inability to urinate
• Blood clots in urine
• Signs of severe dehydration

Causes

Kidney stones form through a complex process involving supersaturation of urine with stone-forming substances, crystal nucleation, and growth. Understanding the various causes helps in both treatment and prevention of recurrent stones.

Primary Mechanisms of Stone Formation

• Supersaturation:
  • Excess concentration of minerals in urine
  • Insufficient fluid to dilute substances
  • pH changes affecting solubility
  • Temperature effects on crystallization
• Lack of inhibitors:
  • Citrate deficiency (natural stone inhibitor)
  • Low magnesium levels
  • Reduced pyrophosphate
  • Abnormal urinary proteins
• Crystal nucleation:
  • Heterogeneous nucleation on cell debris
  • Randall's plaques (calcium deposits)
  • Bacterial involvement in some types

Causes by Stone Type

Calcium Oxalate Stones (75-80%)

• High dietary oxalate (spinach, nuts, chocolate)
• Low calcium intake (paradoxically increases risk)
• Hyperoxaluria (excessive oxalate excretion)
• Hypercalciuria (excessive calcium in urine)
• Low citrate excretion
• Inflammatory bowel disease
• Gastric bypass surgery

Calcium Phosphate Stones (5-10%)

• Renal tubular acidosis
• Hyperparathyroidism
• Urinary tract infections
• Alkaline urine (pH > 7.0)
• Certain medications (topiramate)

Struvite Stones (10-15%)

• Urease-producing bacteria (Proteus, Klebsiella)
• Chronic urinary tract infections
• Urinary stasis or obstruction
• Neurogenic bladder
• Long-term catheter use

Uric Acid Stones (5-10%)

• Persistently acidic urine (pH < 5.5)
• High purine diet (red meat, organ meats)
• Gout or hyperuricemia
• Chronic diarrhea or dehydration
• Diabetes or metabolic syndrome
• Tumor lysis syndrome

Cystine Stones (<1%)

• Cystinuria (genetic disorder)
• Autosomal recessive inheritance
• Defective amino acid transport
• Acidic urine worsens cystine solubility

Metabolic Causes

• Hypercalciuria: Most common metabolic abnormality
  • Absorptive (increased intestinal absorption)
  • Renal (kidney calcium leak)
  • Resorptive (bone demineralization)
• Hyperoxaluria:
  • Primary (genetic)
  • Enteric (malabsorption)
  • Dietary excess
• Hypocitraturia: Low citrate excretion
• Hyperuricosuria: Excessive uric acid excretion

Risk Factors

Multiple factors can increase the likelihood of developing kidney stones. Understanding these risks helps identify high-risk individuals and implement appropriate preventive strategies.

Demographic Risk Factors

• Age: Peak incidence 30-50 years
  • Can occur at any age
  • Increasing in children due to dietary factors
  • Different stone types predominate at different ages
• Sex: Men 2-3 times more likely than women
  • Gender gap narrowing in recent years
  • Estrogen may be protective in premenopausal women
  • Pregnancy increases temporary risk
• Race/Ethnicity:
  • Higher in Caucasians than African Americans
  • Geographic and dietary influences
  • Genetic factors in certain populations
• Geography:
  • "Stone belt" in southeastern United States
  • Hot, dry climates increase risk
  • High altitude regions

Lifestyle and Dietary Factors

• Dehydration: Single most important modifiable risk
  • Low fluid intake
  • Excessive sweating
  • Hot climate exposure
  • Occupations with limited water access
• Diet high in:
  • Sodium (>2,300 mg/day)
  • Animal protein
  • Oxalate-rich foods (with low calcium)
  • Fructose and sugar-sweetened beverages
• Diet low in:
  • Calcium (paradoxically increases risk)
  • Citrus fruits
  • Dietary fiber
  • Potassium
• Obesity: BMI >30 doubles risk
  • Alters urinary chemistry
  • Increases uric acid excretion
  • Associated with metabolic syndrome

Medical Conditions

• Metabolic disorders:
  • Hyperparathyroidism
  • Renal tubular acidosis
  • Cystinuria
  • Primary hyperoxaluria
• Gastrointestinal conditions:
  • Inflammatory bowel disease (Crohn's, UC)
  • Chronic diarrhea
  • Gastric bypass surgery
  • Malabsorption syndromes
• Other conditions:
  • Recurrent UTIs
  • Gout
  • Diabetes type 2
  • Hypertension
  • Polycystic kidney disease
  • Medullary sponge kidney

Medications

• Stone-promoting drugs:
  • Loop diuretics
  • Antacids (calcium-based)
  • Topiramate
  • Vitamin C megadoses (>1000 mg/day)
  • Vitamin D excess
  • Certain antibiotics
  • Protease inhibitors

Family History

• 2.5-fold increased risk with affected first-degree relative
• Genetic factors in calcium metabolism
• Shared dietary and lifestyle habits
• Inherited metabolic disorders

Diagnosis

Accurate diagnosis of kidney stones involves confirming their presence, determining size and location, identifying complications, and when possible, determining stone composition to guide treatment and prevention strategies.

Clinical Evaluation

History

• Characteristic pain pattern and location
• Previous stone episodes
• Family history of stones
• Dietary habits and fluid intake
• Medications and supplements
• Associated medical conditions
• Occupation and climate exposure

Physical Examination

• Costovertebral angle tenderness
• Abdominal examination
• Signs of dehydration
• Temperature (fever suggests infection)
• Patient unable to find comfortable position

Laboratory Tests

Urinalysis

• Findings:
  • Hematuria (85-90% of cases)
  • Crystalluria (specific crystal types)
  • pH (acidic suggests uric acid, alkaline suggests struvite)
  • Pyuria (white blood cells indicate infection)
  • Proteinuria (usually mild)
• Urine culture: If infection suspected

Blood Tests

• Complete blood count (infection, dehydration)
• Serum creatinine (kidney function)
• Electrolytes (calcium, phosphate, uric acid)
• Parathyroid hormone (if hypercalcemia)

Imaging Studies

Non-Contrast CT Scan (Gold Standard)

• Sensitivity and specificity >95%
• Detects all stone types except indinavir
• Determines size, location, and number
• Identifies complications (obstruction, hydronephrosis)
• Can measure stone density (Hounsfield units)
• Rules out alternative diagnoses

Ultrasound

• First-line in pregnancy and children
• No radiation exposure
• Good for detecting hydronephrosis
• Less sensitive for small stones (<5mm)
• Operator dependent
• Point-of-care option in emergency settings

KUB X-ray (Kidneys, Ureters, Bladder)

• Limited sensitivity (45-60%)
• Calcium stones are radiopaque
• Uric acid and cystine stones often radiolucent
• Useful for tracking known stones
• Less expensive than CT

Intravenous Pyelography (IVP)

• Rarely used since CT availability
• Shows filling defects and obstruction
• Requires contrast (allergy/kidney risk)
• Time-consuming

Stone Analysis

• Collection methods:
  • Strain all urine through filter
  • Surgical specimen retrieval
  • Save all passed fragments
• Analysis techniques:
  • X-ray crystallography
  • Infrared spectroscopy
  • Chemical analysis
• Information provided:
  • Stone composition
  • Guide prevention strategies
  • Identify rare stone types

Metabolic Evaluation

For recurrent stone formers or high-risk patients:

• 24-hour urine collection (x2):
  • Volume, pH, creatinine
  • Calcium, oxalate, citrate
  • Uric acid, sodium, potassium
  • Magnesium, phosphate
  • Cystine (if indicated)
• Identifies:
  • Metabolic abnormalities
  • Dietary risk factors
  • Targets for intervention

Treatment Options

Treatment for kidney stones depends on stone size, location, composition, severity of symptoms, and presence of complications. Options range from conservative management for small stones to invasive procedures for larger or complicated stones.

Conservative Management (Stones ≤10mm)

Medical Expulsive Therapy (MET)

• Alpha blockers (tamsulosin):
  • Relaxes ureteral smooth muscle
  • Increases stone passage rate by 30%
  • Reduces time to passage
  • Most effective for distal ureteral stones
• Calcium channel blockers:
  • Alternative to alpha blockers
  • Nifedipine most studied
  • Similar mechanism of action
• Corticosteroids:
  • May reduce ureteral edema
  • Controversial benefit
  • Short course only

Symptom Management

• Pain control:
  • NSAIDs (ketorolac, ibuprofen) - first line
  • Opioids for severe pain
  • Antispasmodics
  • Local heat application
• Hydration:
  • 2-3 liters daily unless contraindicated
  • IV fluids if vomiting
  • Avoid overhydration during acute obstruction
• Antiemetics: For nausea and vomiting
• Antibiotics: If UTI present

Surgical Interventions

Extracorporeal Shock Wave Lithotripsy (ESWL)

• Indications:
  • Stones ≤20mm in kidney or upper ureter
  • Favorable stone composition
  • No obstruction below stone
• Success factors:
  • Stone size and location
  • Composition (best for calcium oxalate)
  • Patient body habitus
  • Kidney anatomy
• Limitations:
  • Less effective for cystine, brushite stones
  • Obesity reduces effectiveness
  • Multiple sessions may be needed

Ureteroscopy (URS)

• Advantages:
  • Direct visualization and removal
  • Higher single-procedure success rate
  • Effective for all stone types
  • Can treat multiple stones
• Techniques:
  • Basket extraction for small stones
  • Laser lithotripsy for larger stones
  • Flexible scopes reach entire kidney
• Stent placement:
  • Often placed post-procedure
  • Prevents obstruction from fragments
  • May cause discomfort

Percutaneous Nephrolithotomy (PCNL)

• Indications:
  • Stones >20mm
  • Staghorn calculi
  • Failed ESWL or URS
  • Complex kidney anatomy
• Procedure:
  • Direct kidney access through back
  • Stone fragmentation and removal
  • Requires general anesthesia
  • 1-2 day hospital stay
• Miniaturized techniques:
  • Mini-PCNL
  • Ultra-mini PCNL
  • Micro-PCNL
  • Reduced morbidity

Medical Dissolution Therapy

Uric Acid Stones

• Urinary alkalinization (pH 6.5-7.0)
• Potassium citrate 20-30 mEq 2-3 times daily
• Sodium bicarbonate alternative
• Allopurinol if hyperuricosuria
• Monitor pH with test strips

Cystine Stones

• Aggressive hydration (>3L daily)
• Urinary alkalinization (pH >7.0)
• Chelating agents (D-penicillamine, tiopronin)
• Dietary sodium restriction

Emergency Interventions

• Indications:
  • Obstructing stone with infection
  • Bilateral obstruction
  • Obstruction in solitary kidney
  • Acute kidney injury
• Options:
  • Ureteral stent placement
  • Percutaneous nephrostomy
  • Urgent stone removal

Follow-up Care

• Repeat imaging to confirm stone clearance
• Stone analysis if retrieved
• Metabolic evaluation for recurrent formers
• Prevention counseling
• Monitor for complications

Prevention

Prevention is crucial as kidney stone recurrence rates approach 50% within 5-10 years without intervention. Strategies should be tailored based on stone composition and individual risk factors.

General Prevention Measures

Hydration - Most Important

• Goal: Urine output >2.5L daily
  • Requires 3-4L fluid intake daily
  • Spread throughout the day
  • Include fluid at bedtime
  • Increase in hot weather or exercise
• Best fluids:
  • Water (primary choice)
  • Citrus juices (lemonade, orange juice)
  • Coffee and tea in moderation
• Avoid or limit:
  • Sugar-sweetened beverages
  • Excessive vitamin C drinks
  • Grapefruit juice

Dietary Modifications

General Guidelines

• Sodium restriction:
  • Limit to 2,300mg daily (1,500mg ideal)
  • Reduces calcium excretion
  • Read food labels
  • Limit processed foods
• Animal protein moderation:
  • Limit to 0.8-1.0 g/kg body weight
  • Choose plant proteins
  • Reduces acid load and citrate excretion
• Calcium intake:
  • Normal calcium diet (1,000-1,200mg daily)
  • Dietary calcium preferred over supplements
  • Take calcium with oxalate-rich foods
  • Avoid calcium restriction

Stone-Specific Dietary Advice

• Calcium oxalate stones:
  • Moderate oxalate intake
  • High-oxalate foods: spinach, rhubarb, nuts
  • Pair calcium with oxalate foods
  • Increase citrate (citrus fruits)
• Uric acid stones:
  • Limit purine-rich foods
  • Reduce red meat, organ meats
  • Limit shellfish and anchovies
  • Alkalinize urine with citrus
• Cystine stones:
  • Very low sodium (<2g daily)
  • Moderate protein restriction
  • Aggressive hydration essential

Medications for Prevention

Thiazide Diuretics

• Reduces urinary calcium excretion
• Hydrochlorothiazide 25-50mg daily
• Chlorthalidone 25mg daily
• Indapamide 1.25-2.5mg daily
• Monitor potassium levels

Alkali Therapy

• Potassium citrate 10-20 mEq 2-3 times daily
• Increases urinary citrate
• Alkalinizes urine
• Prevents calcium and uric acid stones

Allopurinol

• For hyperuricosuria
• 100-300mg daily
• Reduces uric acid production
• May prevent calcium oxalate stones

Lifestyle Modifications

• Weight management:
  • Achieve and maintain healthy BMI
  • Avoid crash diets
  • Gradual weight loss preferred
• Physical activity:
  • Regular moderate exercise
  • Avoid dehydration during exercise
  • Replace fluid losses
• Environmental factors:
  • Stay hydrated in hot climates
  • Air conditioning in extreme heat
  • Occupational risk management

Monitoring and Follow-up

• Annual imaging for high-risk patients
• 24-hour urine collections to assess treatment
• Serum chemistries
• Dietary counseling
• Medication compliance
• Stone recurrence tracking

When to See a Doctor

Seek immediate emergency care for:

• Severe pain unrelieved by over-the-counter medications
• Pain accompanied by fever >101.5°F (38.6°C)
• Persistent vomiting preventing fluid intake
• Blood clots in urine or heavy bleeding
• Complete inability to urinate
• Signs of severe infection (chills, confusion)

Call your doctor promptly for:

• First episode of suspected kidney stone pain
• Blood in urine even without pain
• Recurring flank pain or discomfort
• Difficulty with urination
• Pain lasting more than 24-48 hours
• Recurrent UTI symptoms

Schedule an appointment for:

• Follow-up after passing a stone
• Family history of kidney stones
• Previous stone wanting prevention advice
• Metabolic evaluation if recurrent stones
• Dietary counseling
• Medication side effects

High-risk situations requiring urgent evaluation:

• Solitary kidney with obstruction
• Bilateral kidney stones
• Pregnancy with kidney stone symptoms
• Immunocompromised patients
• Chronic kidney disease patients

Related Conditions

• Urinary Tract Infection
• Chronic Kidney Disease
• Gout
• Hyperparathyroidism
• Inflammatory Bowel Disease
• Renal Tubular Acidosis
• Medullary Sponge Kidney
• Polycystic Kidney Disease

References

1. Pearle MS, Goldfarb DS, Assimos DG, et al. Medical management of kidney stones: AUA guideline. J Urol. 2014;192(2):316-324.
2. Scales CD Jr, Smith AC, Hanley JM, Saigal CS. Prevalence of kidney stones in the United States. Eur Urol. 2012;62(1):160-165.
3. Alelign T, Petros B. Kidney Stone Disease: An Update on Current Concepts. Adv Urol. 2018;2018:3068365.
4. Türk C, Petřík A, Sarica K, et al. EAU Guidelines on Diagnosis and Conservative Management of Urolithiasis. Eur Urol. 2016;69(3):468-474.
5. Fink HA, Wilt TJ, Eidman KE, et al. Medical management to prevent recurrent nephrolithiasis in adults: a systematic review for an American College of Physicians Clinical Guideline. Ann Intern Med. 2013;158(7):535-543.