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Test Code OXU Oxalate, 24 Hour, Urine

Reporting Name

Oxalate, U

Useful For

Monitoring therapy for kidney stones

 

Identifying increased urinary oxalate as a risk factor for stone formation

 

Diagnosis of primary or secondary hyperoxaluria

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Specimen Type

Urine


Specimen Required


Supplies: Diazolidinyl Urea (Germall) 5.0 mL (T822)

Container/Tube: Plastic, 5-mL urine tube (T465) or a clean, plastic aliquot container with no metal cap or glued insert

Specimen Volume: 4 mL

Collection Instructions:

1. Add 5 mL of diazolidinyl urea as a preservative at start of collection or refrigerate specimen during and after collection.

2. Collect urine for 24 hours.

3. Specimen pH should be between 4.5 and 8 and will stay in this range if kept refrigerated. Specimens with pH >8 may indicate bacterial contamination, and testing will be cancelled. Do not attempt to adjust pH as it will adversely affect results.

Additional Information:

1. 24-Hour volume is required.

2. Avoid taking large doses (>2 g orally/24 hours) of vitamin C during specimen collection.

4. See Urine Preservatives-Collection and Transportation for 24-Hour Urine Specimens in Special Instructions for multiple collections.


Specimen Minimum Volume

1 mL

Specimen Stability Information

Specimen Type Temperature Time
Urine Refrigerated (preferred) 14 days
  Frozen  14 days

Reference Values

0.11-0.46 mmol/24 hours

9.7-40.5 mg/24 hours

The reference value is for a 24-hour collection. Specimens collected for other than a 24-hour time period are reported in unit of mmol/L for which reference values are not established.

Day(s) and Time(s) Performed

Monday through Saturday

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

83945

LOINC Code Information

Test ID Test Order Name Order LOINC Value
OXU Oxalate, U In Process

 

Result ID Test Result Name Result LOINC Value
OCATE Oxalate, U 14862-7
OXU1 Oxalate, U 2701-1
TM17 Collection Duration 13362-9
VL15 Urine Volume 3167-4
OX_A Ox Conc (mmol/L) 34349-1
OXCN2 Oxalate Concentration 27222-9

Testing Algorithm

See Hyperoxaluria Diagnostic Algorithm in Special Instructions.

Clinical Information

Oxalate is an end product of glyoxalate and glycerate metabolism. Humans have no enzyme capable of degrading oxalate, so it must be eliminated by the kidney.

 

In tubular fluid, oxalate can combine with calcium to form calcium oxalate stones. In addition, high concentrations of oxalate may be toxic for renal cells.

 

Increased urinary oxalate excretion results from inherited enzyme deficiencies (primary hyperoxaluria), gastrointestinal disorders associated with fat malabsorption (secondary hyperoxaluria), or increased oral intake of oxalate-rich foods or vitamin C.

 

Since increased urinary oxalate excretion promotes calcium oxalate stone formation, various strategies are employed to lower oxalate excretion.

Interpretation

An elevated urine oxalate (>0.46 mmol/24 hours) 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.

Cautions

Ingestion of ascorbic acid (>2 g/24 hours) may falsely elevate the measured urinary oxalate excretion.

 

Do not collect in metal-capped containers.

Clinical Reference

Wilson DM, Liedtke RR: Modified enzyme-based colorimetric assay of urinary and plasma oxalate with improved sensitivity and no ascorbate interference: reference values and sample handling procedures. Clin Chem 1991;37:1229-1235

Method Description

The assay utilizes oxalate oxidase, which oxidizes oxalate to carbon dioxide and peroxide. In the presence of peroxidase, the peroxide oxidatively couples 3-methyl-2-benzothiazolinone and 3-dimethylaminobenzoic acid to form indamine dye, which is measured spectrophotometrically at 580 nm.(Kasidas GP, Rose GA: Continuous-flow assay for urinary oxalate using immobilized oxalate oxidase. Ann Clin Biochem 1985;22:412-419 [A modification of the method])

Analytic Time

3 days

Specimen Retention Time

7 days

Reject Due To

Hemolysis

NA

Lipemia

NA

Icterus

NA

Other

Specimen collected or sent in container with metal cap

NY State Approved

Yes

Method Name

Enzymatic Using Oxalate Oxidase

Urine Preservative Collection Options

Note: The addition of preservative or application of temperature controls must occur within 4 hours of completion of the collection.

Ambient

No

Refrigerate

Yes

Frozen

Yes

50% Acetic Acid

No

Boric Acid

No

Diazolidinyl Urea

Preferred

6M Hydrochloric Acid

No

6M Nitric Acid

No

Sodium Carbonate

No

Thymol

Yes

Toluene

No