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Lab Dept:
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Urine/Stool
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Test Name:
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OXALATE, TIMED URINE
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General Information
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Lab Order Codes:
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OXU
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Synonyms:
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Oxalate, Urine
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CPT Codes:
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83945 - Oxalate
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Test Includes:
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Urine oxalate concentration reported in mmol/specimen.
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Logistics
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Test Indications:
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Useful for monitoring therapy for kidney stones in addition to identifying oxalate in the risk profile for stones. Diagnosis of primary or secondary hyperoxaluria.
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Lab Testing Sections:
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Urine/Stool - Sendouts
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Referred to:
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Mayo Medical Laboratories (Test: OXU/8669)
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Phone Numbers:
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MIN Lab: 612-813-6280
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STP Lab: 651-220-6550
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Test Availability:
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Daily, 24 hours
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Turnaround Time:
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3 - 5 days, test set up Monday - Saturday
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Special Instructions:
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Submit an entire 24-hour urine collection. No preservative. Refrigerate specimen during and after collection. Note: A random sample is acceptable, but no reference ranges are available.
Note: Starting and ending times of collection are required for a timed urine collection and must be documented electronically or on the proper request form.
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Specimen
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Specimen Type:
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Urine, timed collection
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Container:
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Plastic leakproof container (No preservative). Urine GUARD® collection container is preferred for a timed urine sample.
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Draw Volume:
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Submit an entire 24-hour urine collection
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Processed Volume:
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5.0 mL (Minimum: 5.0 mL) urine from a well mixed 24 hr specimen
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Collection:
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For timed urine collections, empty the bladder, discard the voided sample, and note the start time. Collect all urine voided for the specified time period. The specimen must remain covered and protected from light at all times. At the end of the period, note the finishing time; add the last voided sample to the container by emptying the bladder. Bring the refrigerated container to the lab. Make sure all specimens submitted to the laboratory are properly labeled with the patient’s name, medical record number and date of birth.
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Special Processing:
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Lab Staff: Timed specimens: Measure total 24 hour urine volume and record. Adjust pH to 2.5 - 3.0 with 6N HCL within 4 hours of completion of collection and mix well before aliquot is taken.
Send aliquoted specimen in a plastic, 13 mL urine tube or a clean, plastic aliquot container with no metal cap or glued insert.
Send specimen refrigerated. Forward promptly.
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Patient Preparation:
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Avoid taking large doses (≥ 2.0 g orally/24 hours) of vitamin C during specimen collection.
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Sample Rejection:
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Specimen collected or sent in a container with a metal cap is not acceptable, specimens other than urine, mislabeled or unlabeled specimens
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Interpretive
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Reference Range:
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0.11 – 0.46 mmol/specimen (9.7 - 40.5 mg/specimen)
The reference value is for a 24-hour collection. Specimens collected for other than a 24 hour time period are reported in units of mmol/L for which reference values are not established.
Interpretation: An elevated urine oxalate (>0.46 mmol/day) may suggest disease states such as secondary hyperoxaluria (fat malabsorption), primary hyperoxaluria (alanine glyoxalate transferase enzyme deficiency, glyceric dehydrogenase deficiency), idiopathic hyperoxaluria, or excess dietary oxalate or vitamin C intake.
In stone-forming patients high urinary oxalate values, sometimes even in the upper limit of the normal range, are treated to reduce the risk of stone formation.
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Critical Values:
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N/A
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Limitations:
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N/A
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Methodology:
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Enzymatic Using Oxalate Oxidase
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Contraindications:
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Ingestion of ascorbic acid (>2 grams/day) may falsely elevate the measured urinary oxalate excretion.
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References:
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Mayo Medical Laboratories May 2013
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