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Epic Code LAB1230345 Oxalate, 24 Hour, Urine

Additional Codes

Mayo Code: OXU

Epic Code: LAB 1230345

Interface: 55125

Cerner Code: 7165

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Useful For

Monitoring therapy for kidney stones using 24-hour urine collections

 

Identifying increased urinary oxalate as a risk factor for stone formation

 

Diagnosis of primary or secondary hyperoxaluria

Specimen Type

Urine
Laboratory Test Directory Note:

Spectrum Health does not stock toluene as a preservative. Refrigeration during and after urine collection is an acceptable means of urine preservation.


Necessary Information


Twenty-four hour volume is required.



Specimen Required


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

Supplies:

-Diazolidinyl Urea (Germall) 5.0 mL (T822)

-Aliquot Tube, 5 mL (T465)

Container/Tube: Plastic tube 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 (Germall) 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: See Urine Preservatives-Collection and Transportation for 24-Hour Urine Specimens for multiple collections.


Specimen Minimum Volume

1 mL

Forms

If not ordering electronically, complete, print, and send a Renal Diagnostics Test Request (T830) with the specimen.

Specimen Stability Information

Specimen Type Temperature Time Special Container
Urine Refrigerated 14 days

Reject Due To

All specimens will be evaluated at Mayo Clinic Laboratories for test suitability.

Cautions

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

Clinical Information

Oxalate is an end product of glyoxalate and glycerate metabolism. Humans do not have an enzyme capable of degrading oxalate, therefore 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 to 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 (ascorbic acid).

 

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

Method Name

Enzymatic

Report Available

3 to 5 days

Reporting Name

Oxalate, 24 Hr, U

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.

 

Reference values have not been established for patients who are younger than 16 years of age.

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.

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; package insert: Oxalate kit. Trinity Biotech; V 07/2016)

Day(s) Performed

Monday through Saturday

Clinical Reference

1. 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 Jul;37(7):1229-1235

2. Lieske JC, Wang X: Heritable traits that contribute to nephrolithiasis. Urolithiasis. 2019 Feb;47(1):5-10

3. Lieske JC, Turner ST, Edeh SN, Smith JA, Kardia SLR: Heritability of urinary traits that contribute to nephrolithiasis. Clin J Am Soc Nephrol. 2014 May;9(5):943-950

4. Zhao F, Bergstralh EJ, Mehta, RA, et al: Predictors of incident ESRD among patients with primary hyperoxaluria presenting prior to kidney failure. Clin J Am Soc Nephrol. 2016 Jan 7;11(1):119-126

Test Classification

This test has been modified from the manufacturer's instructions. Its performance characteristics were determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information

83945

LOINC Code Information

Test ID Test Order Name Order LOINC Value
OXU Oxalate, 24 Hr, U 14862-7

 

Result ID Test Result Name Result LOINC Value
OCATE Oxalate, 24 Hr, U (mmol/24 hr) 14862-7
OXU1 Oxalate, 24 Hr, U (mg/24 hr) 2701-1
TM17 Collection Duration 13362-9
VL15 Urine Volume 3167-4

Urine Preservative Collection Options

Note: The addition of preservative must occur at the start of collection or application of temperature controls must occur during and after collection.

Ambient

No

Refrigerate

OK

Frozen

No

50% Acetic Acid

No

Boric Acid

No

Diazolidinyl Urea

Preferred

6M Hydrochloric Acid

No

6M Nitric Acid

No

Sodium Carbonate

No

Thymol

No

Toluene

No