Oxalate, Quantitative, 24-Hour Urine
Also known as: Oxalic Acid
Use
Patients who form calcium oxalate kidney stones appear to absorb and excrete a higher portion of dietary oxalate in urine than do normals. Hyperoxaluria is not uncommon in subjects with malabsorption. Twenty-four hour urine collections for oxalate are indicated in patients with surgical loss of distal small intestine, especially those with Crohn's disease. The incidence of nephrolithiasis in patients who have inflammatory bowel disease is 2.6% to 10%.1 Hyperoxaluria is regularly present after jejunoileal bypass for morbid obesity; such patients may develop nephrolithiasis. Used to work up nephrolithiasis.
Special Instructions
Patients must state their age, sex, and the total 24-hour urine volume on the test request form and specimen. Specimens that are submitted without preservative should be acidified to pH ≤3 with 6N HCl before aliquoting. The urine collection period should start by discarding the initial urine void at either 8 a.m. or 8 p.m. The complete collection including the final void at the same time the next day should be properly labeled and mixed.
Limitations
The test may be affected by high ingestion of vitamin C or foods rich in vitamin C, which can increase oxalate excretion. Additionally, low calcium intake or conditions that lead to increased enteric binding of calcium can influence oxalate levels in urine. Rare genetic conditions such as primary hyperoxaluria can also increase endogenous production of oxalates, impacting results. Specific dietary intakes and metabolic states can alter test results, necessitating careful patient preparation and history evaluation.
Methodology
Other
Biomarkers
LOINC Codes
- 2701-1
- 2700-3
- 2701-1
Result Turnaround Time
4-5 days
Related Documents
For more information, please review the documents below
Specimen
Urine
Volume
10 mL aliquot
Minimum Volume
2.5 mL aliquot
Container
Plastic Labcorp 24-hour urine container with 30 mL 6N HCl preservative
Collection Instructions
Collect all urine over a 24-hour period, starting by discarding the initial void and including the final void at the same time the following day. Label with patient's name, and time of start and end of collection. Mix well and ensure pH is ≤3.
Patient Preparation
Avoid vitamin C supplements and vitamin C-rich foods, such as citrus fruits and certain vegetables, for 48 hours prior to collection.
Storage Instructions
Maintain acidified urine at room temperature to prevent crystallization and conversion of ascorbate (vitamin C) to oxalate.
Causes for Rejection
Urine sample received with a pH not ≤3 from a patient on high doses of vitamin C
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 7 days |
| Refrigerated | 7 days |
| Frozen | 8 weeks |
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