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

Workup for Kidney Stones

Initial Diagnostic Evaluation

Ultrasound is the primary diagnostic imaging tool and should not delay emergency care, followed by non-contrast CT for definitive assessment of stone location, size, and burden. 1

Immediate Laboratory Testing

All patients presenting with suspected kidney stones require the following initial workup 1, 2:

• Urinalysis (dipstick and microscopic): Assess for infection indicators, urine pH, and crystal identification 1, 2, 3
• Urine culture: Obtain if urinalysis suggests infection or patient has history of recurrent UTIs 1, 2, 3
• Serum chemistries: Creatinine, ionized calcium, sodium, potassium, uric acid 1, 2, 3
• Complete blood count and C-reactive protein: Required for all emergency presentations 1
• Blood coagulation studies: Can be omitted if no intervention is planned 1

Imaging Algorithm

First-line imaging 1:

• Ultrasound has 45% sensitivity and 88% specificity for renal stones, 45% sensitivity and 94% specificity for ureteral stones 1
• Ultrasound is particularly important in pregnant women and children as the initial modality 1

Second-line imaging 1:

• Non-contrast CT is the gold standard after ultrasound for acute flank pain, providing 93.1% sensitivity and 96.6% specificity 1
• Low-dose CT protocols should be used to minimize radiation exposure while maintaining diagnostic accuracy 1
• KUB radiography (44-77% sensitivity) helps differentiate radioopaque from radiolucent stones and aids in follow-up 1

Special Imaging Considerations

Pregnant patients 1:

• First-line: Ultrasound
• Second-line: MRI
• Last-line: Low-dose CT (only if absolutely necessary)

Pediatric patients 1:

• First-line: Ultrasound
• Second-line: KUB or low-dose non-contrast CT if ultrasound insufficient

Patients requiring PCNL 1:

• Non-contrast CT is mandatory preoperatively (low-dose protocol in children)

Metabolic Evaluation

High-Risk Patients Requiring Comprehensive Workup

24-hour urine collection is recommended for all recurrent stone formers and high-risk first-time formers 2, 3. High-risk features include 2, 3:

• Recurrent stone formation
• Solitary kidney
• Nephrocalcinosis on imaging
• Family history of stones
• Suspected hereditary stone disease (cystinuria, primary hyperoxaluria)

24-Hour Urine Analysis Parameters

The collection should analyze at minimum 2, 3:

• Total urine volume
• Urine pH
• Calcium
• Oxalate
• Uric acid
• Citrate
• Sodium
• Potassium
• Creatinine

Additional parameters 3:

• Urinary cystine (if cystine stones, family history of cystinuria, or suspected cystinuria)
• Suspect primary hyperoxaluria when urinary oxalate exceeds 75 mg/day in adults without bowel dysfunction 3

Two collections are preferred over one for accuracy 3

Stone Analysis

Stone material should be sent for analysis whenever available to guide future prevention strategies 2, 3. This is particularly important for:

• All first-time stone formers 1
• Patients not responding to treatment (stone composition may change over time) 3

Emergency Situations Requiring Immediate Action

Urgent decompression via percutaneous nephrostomy or ureteral stenting is mandatory in cases of 1:

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

Definitive stone treatment must be delayed until sepsis resolves 1. If purulent urine is encountered during endoscopic intervention, abort the procedure, establish drainage, continue antibiotics, and obtain urine culture 2.

Pain Management

NSAIDs (diclofenac, ibuprofen, metamizole) are first-line treatment for renal colic 1. They reduce the need for additional analgesia compared to opioids 1.

Important caveats 1:

• Use lowest effective dose due to cardiovascular and gastrointestinal risks
• May impact renal function in patients with low GFR
• Opioids are second-choice (avoid pethidine; prefer hydromorphine, pentazocine, or tramadol)

Timing of Intervention

If observation with or without medical expulsive therapy fails after 4-6 weeks, offer definitive stone treatment 1. The 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 (ureteroscopy vs. shock-wave lithotripsy vs. continued observation) 1.

Clinical Pitfalls

• Adequate hydration should be maintained, but forced hydration does not accelerate stone passage 2
• CT can be deceiving: Motion artifact can make stones appear larger than actual size; correlate with KUB and ultrasound 4
• Ultrasound sensitivity decreases for stones <3 mm and in non-dilated systems 5
• Routine stenting should not be performed in patients undergoing shock-wave lithotripsy 1