What are the current guidelines for evaluating and managing kidney stones in an adult patient, including initial assessment, imaging choice, treatment based on stone size, criteria for urgent urologic intervention, and secondary prevention strategies?

Kidney Stone Management Guidelines

Initial Assessment and Imaging

For any patient presenting with suspected kidney stones, obtain ultrasound as the first-line imaging modality, followed by non-contrast CT if needed for detailed stone characterization. 1

Immediate Laboratory Evaluation

• Obtain urinalysis (dipstick and microscopic) to assess urine pH, detect infection indicators, and identify crystals 2, 3
• Measure serum creatinine, electrolytes, calcium, and uric acid to identify underlying metabolic conditions and assess renal function 1, 2, 3
• Obtain urine culture if urinalysis suggests infection or patient has recurrent UTIs 2, 3
• Measure CBC and platelet count if significant hemorrhage risk exists or symptoms suggest anemia, thrombocytopenia, or infection 1

Imaging Strategy

• Ultrasound serves as primary diagnostic tool (45% sensitivity, 94% specificity for ureteral stones) 1
• Non-contrast CT is the standard follow-up modality for acute flank pain after ultrasound, providing detailed assessment of stone location, size, density, and anatomy (93.1% sensitivity, 96.6% specificity) 1
• Low-dose CT protocols reduce radiation exposure while maintaining diagnostic accuracy 1
• KUB radiography differentiates radiopaque from radiolucent stones and aids in follow-up monitoring 1
• For pregnant patients, use ultrasound first, MRI second, and low-dose CT only as last resort 1

Urgent Intervention Criteria

In patients with obstructing stones and suspected infection, you must urgently drain the collecting system with a ureteral stent or nephrostomy tube before definitive stone treatment. 1

Emergency Indications

• Obstructing stone with fever or suspected infection requires immediate drainage to prevent urosepsis 1
• If purulent urine is encountered during endoscopic intervention, abort the procedure immediately, establish drainage, and continue antibiotic therapy 3
• Patients with solitary kidney require immediate evaluation 1

Treatment Based on Stone Size and Location

Ureteral Stones <10 mm

Offer medical expulsive therapy (MET) with alpha-blockers for distal ureteral stones <10 mm, with observation and periodic imaging for patients with controlled pain, no sepsis, and adequate renal function. 1, 4

• Both SWL and URS are acceptable first-line options for ureteral stones <10 mm 1
• Patients must have well-controlled pain, no clinical evidence of sepsis, and adequate renal reserve for conservative management 1
• Follow with periodic imaging to monitor stone position and assess for hydronephrosis 1
• Counsel patients that MET is off-label use and discuss associated drug side effects 1

Ureteral Stones >10 mm

For ureteral stones >10 mm, offer surgical treatment (URS or SWL) as most will not pass spontaneously. 1

• URS is associated with lower likelihood of repeat procedures compared to SWL 1
• Never perform blind stone basketing without endoscopic visualization 1
• Do not use electrohydraulic lithotripsy (EHL) as first-line modality due to risk of ureteral perforation 1

Renal Stones ≤20 mm (Non-Lower Pole)

Offer either SWL or URS for symptomatic patients with total non-lower pole renal stone burden ≤20 mm. 1

• Both modalities have acceptable stone-free rates with less morbidity than PCNL 1
• URS results in faster stone-free status due to lower repeat procedure rates compared to SWL 1

Renal Stones >20 mm

Offer PCNL as first-line therapy for symptomatic patients with total renal stone burden >20 mm. 1

• PCNL provides superior stone-free rates (94% vs 75% for URS) and is less invasive than open surgery 1
• Do not offer SWL as first-line therapy for stones >20 mm due to significantly reduced stone-free rates and increased need for multiple treatments 1
• PCNL success is less dependent on stone composition, density, and location compared to other modalities 1

Lower Pole Renal Stones

Offer SWL or URS for symptomatic lower pole stones ≤10 mm, but do not offer SWL as first-line therapy for lower pole stones >10 mm. 1

• For stones ≤10 mm, no significant difference exists in stone-free rates between URS and SWL 1
• For stones >10 mm, endoscopic approaches offer substantial benefit over SWL regarding stone-free rates 1

Preoperative Requirements

Obtain non-contrast CT prior to performing PCNL to minimize infectious complications. 1

Obtain urinalysis prior to any intervention; if clinical or laboratory signs of infection exist, obtain urine culture and administer appropriate antibiotic therapy before proceeding. 1

Administer antimicrobial prophylaxis prior to stone intervention based on prior culture results and local antibiogram. 3

Metabolic Evaluation and Stone Analysis

Stone Composition Analysis

Send all stone material for composition analysis when available to guide prevention strategies. 2, 3

• Stone composition determines specific preventive measures and treatment approaches 2
• Cystine stones indicate genetic cystinuria requiring specific management 2
• Struvite stones indicate infection with urease-producing organisms 2
• Calcium phosphate stones suggest renal tubular acidosis or primary hyperparathyroidism 2

24-Hour Urine Metabolic Testing

Perform comprehensive 24-hour urine metabolic testing in all recurrent stone formers and high-risk first-time stone formers. 2, 3

High-Risk Features Requiring Testing:

• Multiple or bilateral renal calculi 2
• Nephrocalcinosis on imaging 2
• Young age at presentation (≤25 years) 1, 2
• Solitary kidney 2
• Recurrent stones (≥2 episodes) 1
• Strong family history 1, 2

Required 24-Hour Urine Parameters:

• Total urine volume, pH, calcium, oxalate, uric acid, citrate, sodium, potassium, and creatinine 2, 3
• Measure urinary cystine in patients with known or suspected cystine stones 2

Genetic Testing

Consider next-generation sequencing for children, adults ≤25 years, adults >25 years with suspected inherited disorders, or patients with recurrent stones despite appropriate therapy. 1, 2

• Genetic counseling should precede testing 1
• If genetic diagnosis confirmed, offer family screening 1

Secondary Prevention Strategies

Universal Recommendations

Recommend fluid intake achieving at least 2.5 liters of urine output daily to prevent stone recurrence. 3, 5

For patients with calcium stones and hypercalciuria, limit sodium intake and consume 1,000-1,200 mg per day of dietary calcium. 3

Composition-Specific Prevention

• For calcium oxalate stones with hypercalciuria, prescribe thiazide diuretics 2
• For calcium oxalate, cystine, and uric acid stones, alkalinize urine with high fruit/vegetable diet, supplemental citrate, or alkaline mineral waters 5
• For cystine stones specifically, alkalinize urine to pH >7.0 with high fluid intake; consider thiol-binding agents if conservative measures fail 2
• For calcium phosphate and struvite stones, acidify urine with cranberry juice or betaine 5
• For struvite stones, treat underlying infection 2

Follow-Up Monitoring

Obtain single 24-hour urine specimen within six months of initiating treatment to assess response to dietary and/or medical therapy. 2

Obtain annual 24-hour urine specimens after initial follow-up to assess adherence and metabolic response. 2

Perform periodic blood testing to monitor for adverse effects in patients on pharmacological therapy. 2

Adjunctive Measures

Offer alpha-blockers and anti-muscarinic therapy to reduce ureteral stent discomfort. 1

In patients who fail or are unlikely to succeed with SWL and/or URS, offer PCNL, laparoscopic, open, or robotic-assisted stone removal. 1