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 with microscopy, serum chemistries (electrolytes, calcium, creatinine, BUN), and urine culture if infection is suspected. 1, 2

Immediate Laboratory Assessment

Blood Work

• Obtain serum electrolytes, calcium, creatinine, and BUN to identify underlying metabolic conditions and assess renal function 2
• Add complete blood count and C-reactive protein for all emergency presentations 1
• Blood coagulation studies can be omitted if no intervention is planned 1
• Note that stone formers as a group have decreased renal function compared to normal individuals, even with common calcium oxalate stones 3

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 Algorithm

First-Line Imaging

• Ultrasound is the recommended initial imaging tool and should not delay emergency care 1
• Ultrasound has 45% sensitivity and 88% specificity for renal stones, and 45% sensitivity and 94% specificity for ureteral stones 1
• This approach minimizes radiation exposure while providing adequate initial assessment 1

Definitive Imaging

• Non-contrast CT is the gold standard after ultrasound for acute flank pain, providing 93.1% sensitivity and 96.6% specificity 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), obtain additional contrast imaging if further definition of the collecting system and ureteral anatomy is needed 4, 2

Metabolic Evaluation Timing

Acute Presentation

• Basic metabolic panel and urinalysis are sufficient for initial management 2

Comprehensive Metabolic Workup

• Perform 24-hour urine collection for all recurrent stone formers and high-risk first-time formers 1, 2
• High-risk features include: family history of stones, young age at first stone, solitary kidney, or occupational risk 2
• Analyze minimum parameters: total urine volume, pH, calcium, oxalate, uric acid, citrate, sodium, potassium, and creatinine 1, 2
• Two collections are preferred over one for accuracy 1
• Suspect cystinuria or primary hyperoxaluria when urinary oxalate exceeds 75 mg/day in adults without bowel dysfunction 1

Stone Analysis

Send all stone material for analysis whenever available to guide future prevention strategies, particularly for first-time stone formers and patients not responding to treatment 4, 1, 2

The exception is patients with multiple recurrent stones of documented similar composition without clinical or radiographic evidence of compositional change 4

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

Common Pitfalls to Avoid

• Do not rely solely on ultrasound for definitive stone characterization—it has limited sensitivity for detecting stones 1
• Do not skip metabolic evaluation in recurrent stone formers, as this is essential for prevention strategies 1, 2
• Do not delay imaging in emergency presentations, but recognize that ultrasound should be the initial modality to minimize radiation 1
• Recognize that even common stone formers have reduced renal function, so balance risks of obstruction against risks of urological procedures 3
• Maintain adequate hydration, but forced hydration has not been shown to accelerate stone passage 2