Clinics and Departments

Laboratory Services

Lab Dept:

Urine/Stool

Test Name:

OXALATE, TIMED URINE

General Information

Lab Order Codes:

OXU

Synonyms:

Oxalate, Urine

CPT Codes:

83945 - Oxalate

Test Includes:

Urine oxalate concentration reported in mmol/specimen from a 24 hour urine collection.

Logistics

Test Indications:

Useful for monitoring therapy for kidney stones in addition to identifying oxalate in the risk profile for stones. Diagnosis of primary or secondary hyperoxaluria.

Lab Testing Sections:

Urine/Stool - Sendouts

Referred to:

Mayo Medical Laboratories (Test: OXU/8669)

Phone Numbers:

MIN Lab: 612-813-6280

STP Lab: 651-220-6550

Test Availability:

Daily, 24 hours

Turnaround Time:

3 - 5 days, test set up Monday - Saturday

Special Instructions:

Submit an entire 24-hour urine collection. No preservative. Refrigerate specimen during and after collection.

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.

Specimen

Specimen Type:

Urine, timed collection

Container:

Plastic leakproof container (No preservative). Urine GUARD® collection container is preferred for a timed urine sample.

Draw Volume:

Submit an entire 24-hour urine collection

Processed Volume:

5 mL (Minimum: 5 mL) urine from a well mixed 24 hr specimen

Collection:

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.

Special Processing:

Lab Staff: Measure 24 hour urine and document volume. Aliquot 5 mL into a plastic, 13 mL urine tube or a clean, plastic aliquot container with no metal cap or glued insert.

Send specimen refrigerated. Forward promptly.

Patient Preparation:

Avoid taking large doses (≥ 2.0 g orally/24 hours) of vitamin C during specimen collection.

Sample Rejection:

Specimen collected or sent in a container with a metal cap is not acceptable, specimens other than urine, mislabeled or unlabeled specimens

Interpretive

Reference Range:

0.11 – 0.46 mmol/specimen (9.7 - 40.5 mg/specimen)

The reference value is for a 24-hour collection.

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.

Critical Values:

N/A

Limitations:

N/A

Methodology:

Enzymatic Using Oxalate Oxidase

Contraindications:

Ingestion of ascorbic acid (>2 grams/day) may falsely elevate the measured urinary oxalate excretion.

References:

Mayo Medical Laboratories October 2013



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