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Test ID: OROT Orotic Acid, Urine

Reporting Name

Orotic Acid, U

Useful For

Evaluation of the differential diagnosis of hyperammonemia and hereditary orotic aciduria

 

Sensitive indicator of ornithine transcarbamylase (OTC) activity after administration of allopurinol or a protein load to identify OTC carriers

Clinical Information

Urinary excretion of orotic acid, an intermediate in pyrimidine biosynthesis, is increased in many urea cycle disorders and in a number of other disorders involving the metabolism of arginine. The determination of orotic acid can be useful to distinguish between various causes of elevated ammonia (hyperammonemia). Hyperammonemia is characteristic of all urea cycle disorders, but orotic acid is elevated in only some, including ornithine transcarbamylase (OTC) deficiency, citrullinemia, and argininosuccinic aciduria. Orotic acid is also elevated in the transport defects of dibasic amino acids (lysinuric protein intolerance and hyperornithinemia, hyperammonemia, and homocitrullinuria [HHH] syndrome) and is greatly elevated in patients with hereditary orotic aciduria (uridine monophosphate synthase [UMPS] deficiency).

 

OTC deficiency is an X-linked urea cycle disorder that affects both male patients and, due to random X-inactivation, female patients. It is thought to be the most common urea cycle disorder with an estimated incidence of 1:56,000. In OTC deficiency, carbamoyl phosphate accumulates and is alternatively metabolized to orotic acid. Allopurinol inhibits orotidine monophosphate decarboxylase and, when given to OTC carriers (who may have normal orotic acid excretion), can cause increased excretion of orotic acid. When orotic acid is measured after a protein load or administration of allopurinol, its excretion is a very sensitive indicator of OTC activity. A carefully monitored allopurinol challenge followed by several determinations of a patient's orotic acid excretion can be useful to identify OTC carriers, as approximately 20% of OTC variant are not detectable by current molecular genetic testing methods.

Interpretation

The value for the orotic acid concentration is reported. The interpretation of the result must be correlated with clinical and other laboratory findings.

Analytic Time

8 days

Day(s) and Time(s) Performed

Wednesday; 8 a.m.

Clinical Reference

1. Singh RH, Rhead WJ, Smith W, et al: Nutritional management of urea cycle disorders. Crit Care Clin 2005 Oct;21(4 Suppl):S27-35

2. Lee B, Singh RH, Rhead WJ, et al: Considerations in the difficult-to-manage urea cycle disorder patient. Crit Care Clin 2005 Oct;21(4 Suppl):S19-25

3. Brusilow SW, Horwich AL: Urea Cycle Enzymes. In The Online Metabolic and Molecular Bases of Inherited Disease. Edited by D Valle, S Antonarakis, A Ballabio, et al. McGraw-Hill. Accessed 1/13/2020. Available at http://ommbid.mhmedical.com/content.aspx?bookid=2709&sectionid=225084071

4. Webster DR, Becroft DO, van Gennip AH, Van Kuilenburg AP: Hereditary Orotic Aciduria and Other Disorders of Pyrimidine Metabolism. In The Online Metabolic and Molecular Bases of Inherited Disease. Edited by D Valle, S Antonarakis, A Ballabio, et al. , McGraw-Hill. Accessed 1/13/2020. Available at http://ommbid.mhmedical.com/content.aspx?bookid=2709&sectionid=225090376

5. Ah Mew N, Simpson KL, Gropman AL, et al: Urea Cycle Disorders Overview. In GeneReviews. Edited by MP Adam, HH Ardinger, RA Pagon, et al. University of Washington, Seattle, 1993-2020. Updated 2017 Jun 22. Accessed 1/13/2020. Available at: https://www.ncbi.nlm.nih.gov/books/NBK1217

Method Name

Colorimetric

Specimen Type

Urine


Necessary Information


1. Patient's age is required.

2. Provide a reason for referral.



Specimen Required


Supplies: Urine Tubes, 10 mL (T068)

Container/Tube: Plastic, 10-mL urine tube

Specimen Volume: 10 mL

Collection Instructions:

1. Collect a random or timed urine specimen.

2. No preservative.


Specimen Minimum Volume

3 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Urine Frozen 30 days

Reference Values

<2 weeks: 1.4-5.3 mmol/mol creatinine

2 weeks-1 year: 1.0-3.2 mmol/mol creatinine

2-10 years: 0.5-3.3 mmol/mol creatinine

≥11 years: 0.4-1.2 mmol/mol creatinine

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

83921

LOINC Code Information

Test ID Test Order Name Order LOINC Value
OROT Orotic Acid, U 17869-9

 

Result ID Test Result Name Result LOINC Value
8905 Orotic Acid, U 17869-9

Forms

1. Biochemical Genetics Patient Information (T602) in Special Instructions.

2. If not ordering electronically, complete, print, and send an Inborn Errors of Metabolism Test Request (T798) with the specimen.

Mayo Clinic Laboratories | Neurology Catalog Additional Information:

mml-Pediatric, mml-Neurometabolic