What urine lab tests are recommended for kidney stone diagnosis?

Recommended Urine Laboratory Tests for Kidney Stone Diagnosis

For kidney stone diagnosis, clinicians should perform a urinalysis including both dipstick and microscopic evaluation to assess urine pH and identify crystals pathognomonic of stone type, followed by a 24-hour urine collection to evaluate metabolic parameters including volume, pH, calcium, oxalate, uric acid, citrate, sodium, potassium, and creatinine. 1, 2

Initial Screening Evaluation

Urinalysis (First-line)

• Dipstick evaluation: Assesses pH and indicators of infection
• Microscopic evaluation: Identifies crystals specific to stone type
• Urine culture: Indicated if urinalysis suggests urinary tract infection or patient has history of recurrent UTIs 1

Serum Chemistry Tests (Concurrent with urinalysis)

• Electrolytes
• Calcium
• Creatinine
• Uric acid 1
• Intact parathyroid hormone (if primary hyperparathyroidism is suspected) 1

Comprehensive Metabolic Evaluation

For high-risk or interested first-time stone formers and all recurrent stone formers, a more comprehensive metabolic workup is indicated:

24-Hour Urine Collection

• Total volume (target >2.5 L/day)
• pH (critical for determining stone type)
• Calcium (to detect hypercalciuria)
• Oxalate (to detect hyperoxaluria)
• Uric acid (to detect hyperuricosuria)
• Citrate (to detect hypocitraturia)
• Sodium (to assess dietary sodium intake)
• Potassium
• Creatinine (for calculating creatinine clearance) 2

Stone Analysis

When a stone is available, clinicians should obtain a stone analysis at least once using methods such as:

• Fourier-transform infrared spectroscopy (FT-IR)
• X-ray diffraction (XRD) 1, 2

Special Considerations

For Persistent Microscopic Hematuria

Additional testing may include:

• Cystoscopy and imaging to assess for urinary tract growth or new stone formation
• 24-hour urine stone panel to assess for nephrolithiasis and/or microlithiasis
• Kidney biopsy if glomerular disease is suspected 1

For Suspected Stone Disease with Hematuria

• Urinalysis and urine culture to assess for infection
• Imaging studies (non-contrast CT is gold standard) 1, 3

Clinical Pearls and Pitfalls

• Pearl: Stone composition (calcium oxalate, uric acid, struvite, cystine) provides critical information for directing preventive measures 2, 4
• Pitfall: Relying solely on dipstick for hematuria without microscopic confirmation can lead to false positives 1
• Pearl: The most common metabolic abnormalities in calcium stone formers are idiopathic hypercalciuria, unduly acidic urine pH, and hyperuricosuria 4
• Pitfall: Failing to perform a 24-hour urine collection may miss important metabolic abnormalities that could guide prevention strategies 1, 2
• Pearl: Urine pH is particularly important as it helps distinguish between stone types (e.g., persistently acidic urine pH <5.5 predisposes to uric acid stones) 2, 4

By following this systematic approach to laboratory evaluation, clinicians can accurately diagnose kidney stones, identify underlying metabolic abnormalities, and develop targeted prevention strategies to reduce stone recurrence risk and associated morbidity.