How do I evaluate and treat a patient for kidney stones?

Evaluation and Treatment of Kidney Stones

Initial Diagnostic Imaging

For suspected acute kidney stones, start with ultrasound as the primary imaging modality, followed by low-dose non-contrast CT if ultrasound is inconclusive or more detailed information is needed. 1, 2

• Ultrasound should be the first-line imaging with 45% sensitivity and 94% specificity for ureteral stones and 88% specificity for renal stones 1, 2
• Non-contrast CT is the reference standard when ultrasound is inconclusive, offering 93.1% sensitivity and 96.6% specificity, with low-dose protocols maintaining high diagnostic accuracy while reducing radiation exposure 3, 1, 2
• Plain KUB radiography (44-77% sensitivity) helps differentiate radiopaque from radiolucent stones and is useful for follow-up of known stone disease 1, 2

Special Population Considerations

• Pregnant women: Use ultrasound first-line, followed by MRI if needed, with low-dose CT only as last resort 1, 2
• Children: Ultrasound is recommended as first-line imaging 1, 2
• Known stone disease with recurrent symptoms: Non-contrast CT remains the reference standard to assess for stone migration, passage, or complications like infection or perinephric abscess 3

Common pitfall: Ultrasound has low sensitivity (54%) and significantly overestimates stone size in the 0-10mm range, potentially leading to inappropriate counseling in 22% of cases when used alone 4. This is why CT confirmation is critical for management decisions.

Initial Laboratory Evaluation

Obtain urinalysis with microscopy, serum chemistries (electrolytes, calcium, creatinine, uric acid), and urine culture if infection is suspected. 1, 2, 5

• Urinalysis should include both dipstick and microscopic evaluation to assess urine pH, hematuria, signs of infection, and crystal identification 1, 2, 5
• Serum chemistry panel must include electrolytes, calcium, creatinine, and uric acid to identify underlying metabolic conditions 1, 2, 5
• Urine culture is indicated if urinalysis suggests infection or patient has recurrent UTIs 1, 2, 5
• Stone analysis should be performed on any passed or retrieved stone material at least once to determine composition and guide prevention 1, 2, 5

Comprehensive Metabolic Evaluation

Perform 24-hour urine collection for all recurrent stone formers, high-risk first-time formers (multiple/bilateral stones, family history, young age), and interested patients. 1, 2, 5

The 24-hour urine collection should analyze:

• Total urine volume
• Urine pH
• Calcium
• Oxalate
• Uric acid
• Citrate
• Sodium
• Potassium
• Creatinine 1, 2, 5

Additional Metabolic Testing

• Urinary cystine should be measured in patients with known/suspected cystine stones or family history of cystinuria 1, 5
• Serum intact parathyroid hormone if primary hyperparathyroidism is suspected (high or high-normal serum calcium) 1
• Suspect primary hyperoxaluria when urinary oxalate exceeds 75 mg/day in adults without bowel dysfunction 5
• Genetic testing should be considered for early-onset stone disease (≤25 years), suspected inherited disorders, recurrent stones, bilateral disease, or strong family history 1, 2

Imaging Review for Risk Stratification

Review imaging to quantify total stone burden, as multiple or bilateral renal calculi indicate higher recurrence risk. 1, 5

• Nephrocalcinosis on imaging suggests underlying metabolic disorders such as renal tubular acidosis or primary hyperparathyroidism 1, 5
• CT density measurements can classify stones by composition and inner structure, affecting treatment decisions 1

Acute Pain Management

Use NSAIDs as first-line treatment for renal colic, specifically diclofenac 75 mg intramuscularly, as they are more effective than opioids with reduced need for additional analgesia. 2

• Opioids should be second-choice when NSAIDs are contraindicated 2
• Pain control should be maintained for at least six hours 2

Criteria for Immediate Referral/Admission

Immediately refer patients with any of the following: 2

• Fever or signs of infection
• Intractable pain despite adequate analgesia
• Solitary kidney
• Bilateral obstruction
• Acute kidney injury

Clinical context: Recurrent obstruction and infection episodes significantly increase risk for renal failure, particularly in hereditary stone diseases, struvite stones, and infection-related urolithiasis 6. Multiple urological interventions also contribute to chronic renal function deterioration 6.

Follow-up Strategy

For patients managed at home: 2

• Instruct to drink plenty of fluids
• Strain urine to catch any passed stones for analysis
• Contact physician if pain worsens or new symptoms develop
• Make follow-up phone call one hour after initial assessment and analgesia administration 2

Important note: Repeat stone analysis is justified in patients not responding to treatment, as stone composition may change over time 2, 5