What is the recommended initial evaluation and management for a patient with kidney stones, including preferred imaging, treatment based on stone size, and preventive measures?

Kidney Stones: Initial Evaluation and Management

Imaging Strategy

Ultrasound should be performed first in all patients with suspected kidney stones, followed by non-contrast CT if ultrasound is inconclusive or detailed anatomic information is needed. 1, 2

• Ultrasound as first-line imaging provides 45% sensitivity and 94% specificity for ureteral stones and 88% specificity for renal stones, with the critical advantage of no radiation exposure. 1, 2

• Non-contrast CT abdomen and pelvis is the standard second-line modality when ultrasound is inconclusive, offering superior diagnostic accuracy with 93.1% sensitivity and 96.6% specificity. 1, 2

• Low-dose CT protocols should be used to minimize radiation while maintaining diagnostic accuracy. 1, 2

• Point-of-care ultrasound showing moderate to severe hydronephrosis in patients with moderate or high risk of ureteric calculi provides definitive evidence of stone presence without requiring high-dose CT; reserve low-dose CT only when stone size and location are needed for surgical planning. 3

• Plain KUB radiography (sensitivity 44-77%) is most useful for differentiating radiopaque from radiolucent stones and for follow-up imaging, not primary diagnosis. 1, 2

Special Population Imaging

• Pregnant women: Use ultrasound first-line, MRI second-line, and reserve low-dose CT as last resort only. 1, 2

• Children: Ultrasound is strongly recommended as initial study. 2

Laboratory Evaluation

All patients require immediate urinalysis (dipstick and microscopic) plus basic serum chemistry panel. 1, 2

• Urinalysis must assess: urine pH, hematuria, signs of infection, and crystal identification to determine stone type. 1, 2

• Serum chemistry panel should include: electrolytes, calcium, creatinine, uric acid, sodium, potassium, complete blood count, and C-reactive protein if infection suspected. 1, 2

• Urine culture is indicated when urinalysis suggests infection or patient has history of recurrent UTIs. 1, 2

Stone Analysis

Stone compositional analysis should be performed for every first-time stone former when material is available, as results direct preventive therapy and identify underlying metabolic disorders. 1, 2

• Instruct patients to strain urine to catch passed stones for analysis. 2

Management Based on Stone Size

Stones <5mm: Expectation is spontaneous passage without intervention; manage with medical expulsive therapy (MET) and observation. 4

Stones 5-10mm: Initially attempt medical management with MET, but up to 50% may require urologic intervention. 4

Stones >10mm: Should be discussed with urology service immediately as they are unlikely to pass spontaneously. 4

Pain Management

• NSAIDs are first-line treatment for renal colic, preferably diclofenac 75mg intramuscularly or 50-100mg rectally, due to superior effectiveness and reduced need for additional analgesia compared to opioids. 2

• Opioids are second-choice when NSAIDs are contraindicated, though they may worsen nausea and be less effective. 4

• Pain control should be maintained for at least six hours. 2

Immediate Referral Criteria (Red Flags)

The following situations mandate urgent urologic consultation or admission: 1, 2

• Fever or signs of infection with urinary obstruction (requires urgent decompression)
• Obstruction in solitary kidney
• Bilateral obstruction or anuria
• Intractable pain despite adequate analgesia
• Acute kidney injury

Comprehensive Metabolic Evaluation

24-hour urine collection is recommended for high-risk first-time stone formers and all recurrent stone formers. 1, 2

• High-risk features include: multiple or bilateral stones, family history, early age of onset, solitary kidney, nephrocalcinosis on imaging. 1

• 24-hour urine should analyze: total volume, pH, calcium, oxalate, uric acid, citrate, sodium, potassium, and creatinine. 1

• Urinary cystine should be measured in patients with known or suspected cystine stones. 1

• Serum intact parathyroid hormone should be obtained if primary hyperparathyroidism is suspected (elevated or high-normal serum calcium). 1

• Genetic testing should be considered for patients ≤25 years, suspected inherited disorders, recurrent stones (≥2 episodes), bilateral disease, or strong family history. 1, 2

Preventive Measures

Fluid intake of 2.5-3.0 L/day to achieve urine output >2.0-2.5 L/day is the cornerstone of prevention for all stone types. 5

Dietary Modifications

• Calcium intake: Maintain sufficient calcium at 1000-1200 mg/day (do not restrict calcium, as low calcium increases oxalate absorption). 5

• Sodium restriction: Limit to 2-3 grams/day (or 3-5 grams/day of sodium chloride). 5

• Oxalate-rich foods: Limit in patients with calcium oxalate stones. 5

• Animal protein: Limit to 0.8-1.0 g/kg body weight/day but increase plant proteins in patients with calcium and uric acid stones. 5

• Citrus fruits: Increase proportion, particularly for citrate supplementation. 5

• Avoid vitamin C and vitamin D supplements as they can increase stone risk. 5

Lifestyle Modifications

• Maintain normal body mass index. 5
• Fluid compensation for working in high-temperature environments. 5
• Avoid cigarette smoking. 5

Common Pitfalls to Avoid

• Do not use contrast-enhanced CT as first-line study; contrast obscures stones in the collecting system and offers no advantage over non-contrast CT. 2

• Do not assume hydronephrosis absence rules out ureteral stone; negative predictive value is only 65%, and 13% of patients may have alternative diagnoses requiring management. 3

• Do not delay emergency care for imaging in unstable patients. 2