What is the management approach for a patient with possible kidney stones?

Management of Suspected Kidney Stones

Initial Diagnostic Evaluation

All patients with suspected kidney stones require urinalysis with both dipstick and microscopic evaluation to assess urine pH, hematuria, infection, and crystal identification, along with serum chemistries including electrolytes, creatinine, and uric acid. 1

History and Risk Assessment

• Assess pain characteristics: location, intensity, radiation pattern, timing, and aggravating/relieving factors 1
• Identify risk factors including:
  • Personal or family history of stones 1
  • Medical conditions: hyperparathyroidism, renal tubular acidosis, inflammatory bowel disease 1
  • Dietary habits that increase stone risk 1
  • Medications, obesity, metabolic syndrome, diabetes, hypertension 2

Imaging Strategy

• Ultrasound is the first-line imaging modality, particularly for pregnant patients 1
• Non-contrast CT scan should be used to confirm diagnosis and guide treatment decisions when ultrasound is insufficient 1

Acute Management

Pain Control

• NSAIDs are the preferred first-line treatment for renal colic 1
• Opioids may be used as second-line agents for severe pain 1

Conservative Management vs. Intervention

• Medical expulsive therapy (MET) is first-line for uncomplicated distal ureteral stones ≤10 mm 2
• Increase fluid intake immediately to promote stone passage 1
• Instruct patients to strain urine to capture stones for analysis 1
• If stones fail to pass, consider extracorporeal shock wave lithotripsy, ureteroscopy, percutaneous nephrolithotomy, or stent placement depending on stone size, location, and patient factors 2

Emergency Indications

Immediate urologic consultation is required for: 1

• Fever or signs of infection
• Severe uncontrolled pain
• Vomiting causing dehydration
• Signs of urinary obstruction

Stone Analysis and Metabolic Evaluation

Stone analysis should be obtained at least once when material is available to guide prevention strategies. 1

Who Needs Metabolic Testing

High-risk patients requiring 24-hour urine collection include: 1, 2

• Recurrent stone formers
• Family history of stones
• Single kidney
• Malabsorption or intestinal disease
• Young age at first stone

Comprehensive Metabolic Panel

The 24-hour urine collection should analyze: 3

• Total volume, pH
• Calcium, oxalate, uric acid, citrate
• Sodium, potassium, creatinine
• Check serum intact parathyroid hormone if primary hyperparathyroidism suspected 3

Universal Prevention Strategies for All Stone Types

Fluid Intake (Most Critical Intervention)

Prescribe fluid intake sufficient to produce at least 2.5 liters of urine daily 3, 4, 1

• For cystine stones specifically, require ≥4 liters daily to reduce urinary cystine below 250 mg/L 4
• Coffee, tea, wine, and orange juice are associated with lower stone risk 3, 4
• Avoid sugar-sweetened beverages which increase risk 3, 4

Dietary Modifications

Maintain normal dietary calcium intake of 1,000-1,200 mg/day—do NOT restrict calcium 3, 4, 1

• A 5-year RCT demonstrated 51% lower recurrence with normal calcium (1,200 mg/day) versus low calcium (400 mg/day) diet 3
• Restricting dietary calcium paradoxically increases stone risk by increasing intestinal oxalate absorption 1
• Avoid calcium supplements, which increase stone risk by 20% 3

Limit sodium intake to 2,300 mg (100 mEq) daily 3, 4

• Sodium restriction reduces urinary calcium excretion 3

For calcium oxalate stones, limit oxalate-rich foods while maintaining normal calcium consumption 4, 1

Pharmacologic Management Based on Stone Composition

Calcium Stones with Hypercalciuria

Thiazide diuretics should be offered as standard therapy 3, 4

Effective dosing regimens: 3, 4

• Hydrochlorothiazide: 25 mg twice daily OR 50 mg once daily
• Chlorthalidone: 25 mg once daily
• Indapamide: 2.5 mg once daily

Monitor for hypokalemia and provide potassium supplementation as needed 3, 4

Calcium Stones with Hypocitraturia

Potassium citrate therapy should be offered at 30-100 mEq per day 3, 4

• Prospective RCTs demonstrate reduced recurrence of calcium stones 3
• Maintain urinary pH between 6.0-6.5 to optimize calcium solubility while avoiding calcium phosphate precipitation 4
• Monitor for hyperkalemia 3

Calcium Oxalate Stones with Hyperuricosuria

Allopurinol should be offered to patients with hyperuricosuria (>800 mg/day) and normal urinary calcium 3, 4

• Prospective RCT demonstrated reduced recurrence in this specific population 3

Monitoring and Follow-Up

Obtain 24-hour urine specimen within 6 months of initiating treatment to assess response 3, 4

• Annual 24-hour urine specimens recommended for long-term follow-up 4
• Monitor for medication adverse effects: hypokalemia with thiazides, hyperkalemia with potassium citrate 3

Common Pitfalls to Avoid

• Do not restrict dietary calcium—this increases stone risk 3, 1
• Do not recommend calcium supplements—use dietary sources only 3
• Do not prescribe allopurinol for patients with normal uric acid excretion—it only benefits those with hyperuricosuria >800 mg/day 3
• Do not forget to check potassium levels in patients on thiazides or potassium citrate 3, 4