Comprehensive Workup for Renal Stones
The recommended workup for patients with renal stones should include a detailed medical and dietary history, serum chemistries, urinalysis, stone analysis when available, and appropriate imaging studies to quantify stone burden. 1
Initial Evaluation
History and Physical Assessment
- Obtain detailed medical history focusing on:
- Previous stone episodes
- Family history of stones
- Medical conditions associated with stone disease (hyperparathyroidism, gout, inflammatory bowel disease)
- Medications that may predispose to stone formation
- Dietary habits related to stone risk factors
Dietary History
- Assess daily intake of:
- Fluids (amount and specific beverages)
- Protein (types and amounts)
- Calcium intake
- Sodium consumption
- High oxalate-containing foods
- Fruits and vegetables
- Over-the-counter supplements 1
Laboratory Testing
Basic Laboratory Evaluation
Serum chemistries:
- Electrolytes
- Calcium (to screen for hyperparathyroidism)
- Creatinine (to assess renal function)
- Uric acid 1
Urinalysis:
- Dipstick and microscopic evaluation
- Urine pH assessment
- Indicators of infection
- Crystal identification 1
Urine culture:
- When urinalysis suggests infection
- In patients with recurrent UTIs 1
Imaging Studies
- Non-contrast CT scan is the gold standard for detection and characterization of stones 2
- Review available imaging to quantify stone burden (size, number, location)
- Assess for presence of nephrocalcinosis, which may indicate underlying metabolic disorders 1
Advanced Metabolic Evaluation
Stone Analysis
- When a stone is available, obtain stone analysis at least once
- Stone composition provides critical information about underlying metabolic or genetic abnormalities:
- Uric acid stones suggest acidic urine pH
- Cystine stones indicate cystinuria
- Struvite stones suggest infection 1
Additional Testing for High-Risk Patients
Perform additional metabolic testing in:
- High-risk first-time stone formers
- Recurrent stone formers
- Patients with nephrocalcinosis
- Multiple or bilateral stones at presentation 1
24-Hour Urine Collection
Collect one or two 24-hour urine samples (two collections preferred)
Analyze for:
- Total volume
- pH
- Calcium
- Oxalate
- Uric acid
- Citrate
- Sodium
- Potassium
- Creatinine 1
Additional parameters for specific conditions:
- Urinary cystine in patients with known cystine stones, family history of cystinuria, or suspected cystinuria
- Consider primary hyperoxaluria when urinary oxalate exceeds 75 mg/day in adults without bowel dysfunction 1
Specialized Testing
- Serum intact parathyroid hormone (PTH) when primary hyperparathyroidism is suspected (especially with high or high-normal serum calcium) 1
- Genetic testing when primary hyperoxaluria is suspected, particularly in patients with eGFR <30 ml/min/1.73 m² and hyperoxalemia 1
Follow-Up Evaluation
Monitoring Stone Progression
- Regular imaging surveillance to monitor:
- Stone growth
- Development of obstruction
- Changes in renal function 3
- Ultrasound in combination with radiography is recommended for follow-up to reduce radiation exposure 2
Treatment Response Assessment
- For patients on medical therapy, periodic metabolic evaluation to assess response
- Repeat 24-hour urine collections to monitor improvement in urinary risk factors
Common Pitfalls and Caveats
Single urine collection may be insufficient: Variations in diet and hydration can affect results; two collections are preferred 1
Inadequate stone analysis: Failure to analyze available stones misses critical diagnostic information 1
Overlooking hyperparathyroidism: Always check serum calcium and consider PTH when calcium is high or high-normal 1
Ignoring dietary factors: Detailed dietary assessment is essential for targeted interventions 1
Insufficient imaging: CT provides superior information about stone composition, size, and location compared to ultrasound alone 2
Missing underlying metabolic disorders: Nephrocalcinosis or multiple stones should prompt thorough metabolic evaluation 1
By following this comprehensive approach to the workup of renal stones, clinicians can identify underlying causes, assess risk factors for recurrence, and develop targeted prevention strategies to reduce morbidity and improve quality of life.