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
For information see Hyperoxaluria Diagnostic Algorithm.
Enzymatic
Oxalate
For information see Hyperoxaluria Diagnostic Algorithm.
Urine
24-hour volume (in milliliters) is required.
| Question ID | Description | Answers |
|---|---|---|
| TM17 | Collection Duration | |
| VL15 | Urine Volume |
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.
If not ordering electronically, complete, print, and send a Renal Diagnostics Test Request (T830) with the specimen.
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 additive) | No |
| Refrigerate (No additive) | OK |
| Frozen (No additive) | 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 |
1 mL
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Urine | Ambient | 72 hours | |
| Refrigerated (preferred) | 14 days | ||
| Frozen | 14 days |
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
For information see Hyperoxaluria Diagnostic Algorithm.
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.
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.
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.
Ingestion of ascorbic acid (>2 g/24 hours) may falsely elevate the
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;37(7):1229-1235
2. Lieske JC, Wang X. Heritable traits that contribute to nephrolithiasis. Urolithiasis. 2019;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;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;11(1):119-126
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 600 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 11/2017)
Monday through Saturday
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.
83945
| Test Id | Test Order Name | Order LOINC Value |
|---|---|---|
| OXU | Oxalate, 24 Hr, U | 14862-7 |
| Result Id | Test Result Name |
Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
|
|---|---|---|
| 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 |