What laboratory tests are needed for a patient with kidney stones?

Laboratory Tests for Kidney Stone Patients

For patients with kidney stones, essential laboratory tests include serum electrolytes, calcium, creatinine, uric acid, urinalysis with microscopic evaluation, and urine culture if infection is suspected. 1, 2

Initial Laboratory Evaluation

• Serum chemistries:

  • Electrolytes (sodium, potassium, chloride, bicarbonate) 1, 2
  • Calcium 1, 2
  • Creatinine 1, 2
  • Uric acid 1, 2
  • Intact parathyroid hormone (if primary hyperparathyroidism is suspected - when serum calcium is high or high normal) 1, 3

• Urine studies:

  • Urinalysis with dipstick and microscopic evaluation (to assess pH, indicators of infection, and identify crystals) 1, 2
  • Urine culture (if urinalysis suggests infection or patient has history of recurrent UTIs) 1, 2
  • Stone analysis (when a stone is available) 1, 3

Comprehensive Metabolic Evaluation

For high-risk or interested first-time stone formers and all recurrent stone formers, 24-hour urine collection should be performed to analyze:

• Total urine volume 1, 2
• Urine pH 1, 2
• Calcium 1, 2
• Oxalate 1, 2
• Uric acid 1, 2
• Citrate 1, 2
• Sodium 1, 2
• Potassium 1, 2
• Creatinine 1, 2
• Urinary cystine (if cystine stones are known or suspected, or if family history of cystinuria exists) 1, 2

Special Considerations

• Two 24-hour urine collections are preferred over a single collection for more accurate assessment 1, 2
• Primary hyperoxaluria should be suspected when urinary oxalate exceeds 75 mg/day in adults without bowel dysfunction 1
• Imaging studies (non-contrast CT scan) should be reviewed to quantify stone burden and identify patients at higher risk of recurrence 1, 3
• Nephrocalcinosis on imaging suggests underlying metabolic disorders that may require additional testing 1

Clinical Pearls and Pitfalls

• Failure to perform stone analysis when available may miss important diagnostic information about underlying metabolic or genetic abnormalities 1, 2
• Inadequate 24-hour urine collection (incomplete collection or improper handling) can lead to inaccurate results and inappropriate treatment 2
• Multiple or bilateral renal calculi at initial presentation may indicate higher risk of recurrence and warrant more comprehensive evaluation 1
• Patients on certain medications (protease inhibitors, some antibiotics, diuretics) have increased risk of stone formation and require closer monitoring 4