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Test ID ROXU Oxalate, Pediatric, Random, Urine

Reporting Name

Oxalate, Pediatric, Random, 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

 

A timed 24-hour urine collection is the preferred specimen for measuring and interpreting this urinary analyte. Random collections normalized to urinary creatinine may be of some clinical use in patients who cannot collect a 24-hour specimen, typically small children. Therefore, this random test is offered for children <16 years old.

Specimen Type

Urine


Specimen Required


Container/Tube: Plastic, 10-mL urine tube (T068)

Specimen Volume: 7 mL

Collection Instructions:

1. Collect a random urine specimen.

2. No preservative.

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. A timed 24-hour urine collection is the preferred specimen for measuring and interpreting this urinary analyte. Random collections normalized to urinary creatinine may be of some clinical use in patients who cannot collect a 24-hour specimen, typically small children. Therefore, this random test is offered for children <16 years old.

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


Specimen Minimum Volume

6 mL

Specimen Stability Information

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

Reference Values

No established reference values

Day(s) and Time(s) Performed

Monday through Saturday; 1 p.m.

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
ROXU Oxalate, Pediatric, Random, U In Process

 

Result ID Test Result Name Result LOINC Value
OXCON Oxalate, Pediatric, Random, U 15086-2
OXCO2 Oxalate Concentration 2700-3
CREA8 Creatinine Concentration 2161-8
RATO7 Oxalate/Creatinine Ratio 13483-3

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/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.

 

The urinary oxalate creatinine ratio varies widely in young children from <0.35 mmol/mL at birth to <0.15 mmol/mL at 1 year to <0.10 mmol/mL at 10 years and <0.05 mmol/mL at 20 years of age (see table below).(1)

Oxalate/Creatinine (mg/mg)

Age (year)

95th Percentile

0-0.5

<0.175

0.5-1

<0.139

1-2

<0.103

2-3

<0.08

3-5

<0.064

5-7

<0.056

7-17

<0.048

Clinical Reference

1. Matos V, Van Melle G, Werner D et al: Urinary oxalate and urate to creatinine ratios in a healthy pediatric population. Am J Kidney Dis 1999;34:e1

2. 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

Analytic Time

3 days; Excess capacity for this test is limited. Therefore, if sample volume exceeds analyzer capacity, the turnaround time will increase. Please contact the lab supervisor for an estimate.

Method Name

Enzymatic Using Oxalate Oxidase