Suitable Specimen Types

  • Plain Spot Urine
5 mL

Specimen Transport

Send frozen.

Sample Processing in Laboratory

Please transport sample to BHH as soon as possible.

Sample Preparation

Freeze sample prior to sending to Ref Lab

Turnaround Time

2 weeks

Sample Stability

-20 ºC

Orotic Acid (urine)

General Information

Pyrimidine biosynthesis, in which orotic acid is a major intermediate, is regulated at the level of carbamylphosphate synthetase II (CPS II), the enzyme catalyzing the first reaction in this pathway. The isoenzyme CPS I (a mitochondrial enzyme) catalyzes the production of carbamylphophate during the process of urea synthesis. Under conditions in which mitochondrial carbamylphosphate accumulates (e.g. in urea cycle disorders), cytosolic carbamylphosphate levels rise and urine orotic acid excretion increases. This may be recognised in organic acid analysis, but orotic acid is a charged nitrogen species which has very limited solubility in organic solvents and the amount detected by routine GC-MS is a fraction of the actual concentration. Therefore accurate quantification of orotic acid requires LC-MS/MS analysis.

Urine orotic acid analysis is one of the key investigations in significant hyperammonaemia. Increased urinary excretion of orotic acid is a feature of four IMDs involving the urea cycle:

  • Ornithine Transcarbamylase (OTC) Deficiency
  • Citrullinaemia
  • Argininosuccinic aciduria
  • Argininaemia

In the past, an allopurinol loading test has been used to tests heterozygous female carriers for OTC deficiency however, this is no longer used as mutational analysis provides more accurate information.

Patient Preparation



None Given

Reference Range

Provided by Reference Laboratory

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Protection of Personal Information – Laboratory Medicine comply with the Trust Data Protection Policy and have procedures in place to allow the Directorate and it’s employees to comply with the Data Protection Act 1998 and associated best practice and guidance.

The Trust Laboratories at Heartlands Hospital, Good Hope Hospital and Solihull Hospital were awarded UKAS (United Kingdom Accreditation Service) accreditation to the internationally recognised ISO 15189 standard in May 2015. For a list of accredited tests and other information please visit the test database
Tests not appearing on this scope are either under consideration or in the process of accreditation and so currently remain outside of our scope of accreditation. However, these tests have been validated to the same high standard as accredited tests and are performed by the same trained and competent staff.

For further information contact Louise Fallon, Quality Manager, 0121 424 1235

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