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HelpTest Code OXU Oxalate, 24 Hour, Urine
Reporting Name
Oxalate, 24 Hr, UUseful 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
UrineNecessary Information
24-hour volume (in milliliters) is required.
Specimen Required
Patient Preparation: For 24 hours before, as well as during the collection process, patient should not take large doses (>2 g orally/24 hours) of vitamin C.
Supplies:
-Diazolidinyl Urea (Germall) 5.0 mL (T822)
-Sarstedt Aliquot Tube, 5mL (T914)
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. Mix container thoroughly and aliquot urine into plastic vial.
4. Specimen pH should be between 4.5 and 8 and will stay in this range if kept refrigerated. Specimens with pH above 8 indicate bacterial contamination, and testing will be canceled. 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
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Urine | Refrigerated (preferred) | 14 days | |
| Frozen | 14 days | ||
| Ambient | 72 hours |
Special Instructions
Reference Values
0.11-0.46 mmol/24 h
9.7-40.5 mg/24 h
The reference value is for a 24-hour collection. Specimens collected for other than a 24-hour 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.
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 |
Testing Algorithm
For information see Hyperoxaluria Diagnostic Algorithm.
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 kidney 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.
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.
Reject Due To
All specimens will be evaluated at Mayo Clinic Laboratories for test suitability.Method Name
Enzymatic
Forms
If not ordering electronically, complete, print, and send a Renal Diagnostics Test Request (T830) with the specimen.