Sign in →

Test Code 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

Performing Laboratory

Mayo Clinic Laboratories in Rochester

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

Day(s) and Time(s) Performed

Wednesday; 8 a.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

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

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.

Analytic Time

8 days

Reject Due To

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

NY State Approved

Yes

Method Name

Colorimetric

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.