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Oxalate, Urine 24-Hour

Oxalate, 24-hr urine

Test Codes

Antrim #13190, EPIC: LAB5872, SOFT: OXA24

Department

Special Chemistry

Instructions

• Excessive amounts of oxalate rich foods or Vitamin C can interfere with the assay and should be avoided 48 hours prior to urine collection.
• Please refer to the Specimen Collection Manual for instructions on 24 Hour Urine Collection:
  • Urine 24 Hour Collection - Inpatient
  • Urine 24 Hour Collection - Outpatient/Outreach

Specimen Collection Criteria

Collect (preferred specimen): 24 hour urine sample with 15 mL of 6N Hydrochloric Acid added prior to the start of collection.
Also acceptable [if collected with other tests (Stone Former)]: 24 hour urine collection with no preservative, acidified in the Laboratory upon receipt.

• Keep 24 hour urine specimen iced or refrigerated during collection.
• Include start and end dates and times for the collection period on the specimen container.

Urine Preservative Options
No Preservative	6N Hydrochloric Acid	Boric Acid (10g)	Sodium Carbonate	50% Acetic Acid
Acceptable	Preferred	Unacceptable	Unacceptable	Unacceptable

Preparation for Courier Transport

Maintain specimens refrigerated (2-8°C or 36-46°F) prior to transport.

Rejection Criteria

• Random urine specimens.
• Samples not kept refrigerated (2-8°C or 36-46°F).
• Samples not collected and processed as indicated.

In-Lab Processing

Measure total volume of 24 hour urine specimen. Record total volume and collection start and end dates and times in the LIS system. Aliquot a minimum of 10 mL from the well-mixed 24 hour urine collection. The pH of 24-hour urine collection with added preservative should be 4.0 or lower. Adjust the pH of the aliquot to between 1.0 and 3.0. The specimen will be heated to 56°C for 15 minutes in Chemistry during sample processing, prior to storage. Refrigerate aliquot prior to analysis.  the sample will, again, be heated to 56°C in Special Testing, prior to analysis, to re-dissolve the oxalate.

Storage

Specimen Stability for Testing:

Room Temperature (20-26°C or 68-78.8°F): Unacceptable
Refrigerated (2-8°C or 36-46°F): 21 days
Frozen (-20°C/-4°F or below): 21 days

Specimen Storage in Department Prior to Disposal:

Refrigerated (2-8°C or 36-46°F): 7 days

Laboratory

Royal Oak Special Testing Laboratory

Performed

Varies, once per week.
Results available within 7 days.

Reference Range

Adult Males: 7-44 mg/24 hours.
Adult Females: 4-31 mg/24 hours.
Children: 13-38 mg/24 hours.

Test Methodology

Enzymatic using oxalate oxidase.

Interpretation

Oxalate in urine may arise either as an end-product of intermediary metabolism or from dietary sources. Decreased oxalate excretion is associated with hyperglycemia and hyperglycinuria. Increased excretion of oxalate is attributed to increased (1) ingestion of oxalate precursors or oxalate rich foods (2) formation of oxalate as in primary hyperoxaluria and (3) absorption of oxalate in a number of gastrointestinal disorders that produce severe fat malabsorption. Formation of the sparingly soluble calcium salt of oxalate in the urinary tract is considered the major factor in urolithiasis (stone formation).

Excessive amounts of oxalate rich foods or Vitamin C (exceeding 16 mmol/L) can interfere with the assay and should be avoided 48 hours prior to urine collection.

Clinical Utility

Urinary oxalate is useful in assessing the risk of renal calcium stone formation (urolithiasis) and is determined as part of the Stone Former Panel.

CPT Codes

83945
LOINC: 2701-1, 27222-9

Contacts

Last Updated

4/10/2024