What is the recommended workup for kidney stones?

Recommended Workup for Kidney Stones

The recommended workup for kidney stones should include serum chemistries (electrolytes, calcium, creatinine, uric acid), urinalysis, urine culture if infection is suspected, stone analysis when available, and appropriate imaging to quantify stone burden. 1, 2

Initial Evaluation

History and Physical Assessment

• Assess for symptoms: renal colic, dysuria, urinary frequency, hematuria, fever, flank pain, groin pain
• Identify risk factors:
  • Medical conditions: obesity, metabolic syndrome, diabetes, hypertension
  • Family history of stones
  • Previous stone episodes
  • Anatomical abnormalities of kidneys or ureters

Laboratory Testing

1. Basic Laboratory Tests:

   • Serum chemistries: electrolytes, calcium, creatinine, uric acid 1
   • Urinalysis: pH, crystals, blood, signs of infection 1
   • Urine culture: if urinalysis suggests infection or patient has recurrent UTIs 1
   • Serum intact parathyroid hormone: if primary hyperparathyroidism is suspected (especially with high or high-normal serum calcium) 1

2. Stone Analysis:

   • Should be performed at least once when a stone is available 1, 2
   • Fourier-transform infrared spectroscopy (FT-IR) or X-ray diffraction (XRD) are preferred methods 2
   • Chemical analysis alone is not recommended due to high error rates 2

Caution: Failing to obtain stone analysis can lead to inadequate treatment and prevention strategies 2

Imaging

• Obtain imaging studies to quantify stone burden 1
• Renal ultrasonography is recommended as first-line imaging modality 3
• Consider non-contrast CT scan for more detailed evaluation

Advanced Metabolic Evaluation

Who Needs Advanced Testing?

Advanced metabolic testing should be performed in:

• High-risk first-time stone formers 1
• Recurrent stone formers 1
• Patients with comorbidities or large stones 4

High-risk factors include:

• Multiple or bilateral renal calculi at initial presentation 1
• Nephrocalcinosis
• Family history of stones
• Single kidney
• Malabsorption or intestinal disease 3

24-Hour Urine Collection

• Should consist of one or two 24-hour urine collections obtained on a random diet 1
• Parameters to analyze:
  • Total volume
  • pH
  • Calcium
  • Oxalate
  • Uric acid
  • Citrate
  • Sodium
  • Potassium
  • Creatinine 1, 2
  • Cystine (if cystinuria is suspected) 1

Important: Two 24-hour urine collections are preferred over a single collection to account for daily variations 1

Follow-Up Evaluation

• Periodic imaging (typically ultrasound) to monitor for stone growth or new stone formation 2
• Repeat metabolic testing to assess response to treatment and dietary modifications
• Adjust preventive measures based on follow-up results

Common Pitfalls to Avoid

1. Relying solely on chemical analysis for stone composition 2
2. Failing to send stone material for analysis 2
3. Inadequate follow-up, especially for infection stones 2
4. Not performing metabolic evaluation in high-risk patients
5. Missing underlying metabolic disorders (e.g., primary hyperparathyroidism, renal tubular acidosis)

By following this comprehensive workup approach, clinicians can identify underlying metabolic abnormalities, determine stone composition, and develop targeted prevention strategies to reduce the risk of recurrent stone formation and associated complications.