What is the initial workup and management for a patient with suspected kidney stones?

Initial Workup for Suspected Kidney Stones

Begin with ultrasound as the primary imaging modality, followed by non-contrast CT for definitive stone characterization, while simultaneously obtaining urinalysis, serum chemistries, and renal function tests. 1, 2

Immediate Laboratory Assessment

Blood Work

• Obtain serum electrolytes, calcium, creatinine, and BUN to identify underlying metabolic conditions and assess renal function 2
• Complete blood count and C-reactive protein are required for all emergency presentations 1
• Blood coagulation studies can be omitted if no intervention is planned 1

Urine Studies

• Perform urinalysis with both dipstick and microscopic evaluation to assess urine pH, detect infection indicators, and identify crystals suggesting stone type 2
• Collect urine culture if urinalysis suggests infection or if the patient has recurrent urinary tract infections 2

Imaging Strategy

First-Line Imaging

• Ultrasound should be the initial imaging modality (sensitivity 45%, specificity 88% for renal stones; sensitivity 45%, specificity 94% for ureteral stones) 1
• Ultrasound should not delay emergency care 1

Definitive Imaging

• Non-contrast CT is the gold standard after ultrasound for acute flank pain (sensitivity 93.1%, specificity 96.6%) 1
• Use low-dose CT protocols to minimize radiation exposure while maintaining diagnostic accuracy 1
• In patients with complex stones or anatomy (horseshoe kidney, pelvic kidney, duplicated collecting system, staghorn stones), additional contrast imaging may be needed for better definition of collecting system and ureteral anatomy 3, 2

Stone Analysis

• Send all stone material for analysis to guide future prevention strategies 3, 1, 2
• The only exception is patients with multiple recurrent stones of documented similar composition without clinical or radiographic evidence of compositional change 3

Metabolic Evaluation Timing

Immediate vs. Delayed Assessment

• Basic metabolic assessment (serum chemistries, urinalysis) should be obtained during initial presentation 2
• Comprehensive 24-hour urine collection is recommended for all recurrent stone formers and high-risk first-time formers 1, 2
• The 24-hour collection should analyze: total volume, pH, calcium, oxalate, uric acid, citrate, sodium, potassium, and creatinine 1, 2
• Two collections are preferred over one for accuracy 1
• Suspect urinary cystine and primary hyperoxaluria when urinary oxalate exceeds 75 mg/day in adults without bowel dysfunction 1

Emergency Situations Requiring Immediate Action

Urgent decompression via percutaneous nephrostomy or ureteral stenting is mandatory in these scenarios: 1

• Sepsis with obstructed kidney
• Anuria with obstructed kidney
• Solitary kidney with obstruction
• Fever with obstruction

Pain Management

• NSAIDs (diclofenac, ibuprofen, metamizole) are first-line treatment for renal colic, reducing need for additional analgesia compared to opioids 1
• Use the lowest effective dose due to cardiovascular and gastrointestinal risks 1
• Avoid NSAIDs in patients with low GFR due to impact on renal function 1
• Maintain adequate hydration, though forced hydration has not been shown to accelerate stone passage 2

Common Pitfalls and Caveats

Renal Function Considerations

• Stone formers as a group have decreased renal function compared to normal individuals, even common calcium oxalate stone formers 4
• All efforts must minimize renal injury, balancing obstruction risks against procedural risks 4
• Normal-sized kidneys on ultrasound do not exclude chronic kidney disease, as renal size is initially preserved in diabetic nephropathy or infiltrative disorders 3

Timing of Intervention

• If observation with or without medical expulsive therapy fails after 4-6 weeks, offer definitive stone treatment 1
• Maximum conservative therapy interval should not exceed 6 weeks to avoid irreversible kidney injury 1
• Repeat imaging prior to intervention is recommended if symptoms have changed, as stone position may influence treatment approach 1