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Unit Code 8905:
Orotic Acid, Urine

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Useful For

Evaluation of the differential diagnosis of hyperammonemia

and hereditary orotic aciduria.

 

When orotic acid is measured after a protein load or allopurinol

administration, excretion of orotic acid is a very sensitive

indicator of ornithine transcarbamylase (OTC) activity.  The

allopurinol test can be used to determine whether a female is

heterozygous for X-linked OTC deficiency when an OTC deficient

patient has been identified in her family.

Clinical Information

Orotic acid is an intermediate in pyrimidine biosynthesis.

 

The major clinical application of the determination of orotic acid is in

the differential diagnosis of hyperammonemia because increased urinary

excretion of orotic acid is observed in most inborn errors of the urea

cycle as well as the transport defects of dibasic amino acids (lysinuric

protein intolerance, and hyperornithinemia, hyperammonemia,

homocitrullinuria [HHH] syndrome).  Orotic acid is formed from

carbamoyl phosphate which accumulates in these urea cycle

disorders.  Accordingly, deficiency of the first enzyme in the urea

cycle carbamoyl phosphate synthetase and of N-acetylglutamate

synthetase do not present with orotic aciduria.

 

Patients with hereditary orotic aciduria (uridine monophosphate

synthase [UMPS] deficiency) also excrete orotic acid excessively.

This disorder is characterized by megaloblastic anemia which

becomes apparent weeks to months after birth, failure to thrive, and

developmental delay.

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

> or = 11 years:  0.4-1.2 mmol/mol creatinine

Interpretation

The value for the orotic acid concentration is reported. The

interpretation of the result must be correlated with clinical and

other laboratory findings.

Cautions

No significant cautionary statements

Clinical Reference

1.   Brusilow SW, Horwich AL:  Urea cycle enzymes. In The Metabolic

      and Molecular Bases of Inherited Disease. 8th edition. Edited by

      CR Scriver, AL Beaudet, WS Sly, et al. McGraw-Hill Book Company,

      2001, pp 1909-1964

 

2.   Webster DR, Becroft DMO, van Gennip AH, van Kuilenberg ABP:

      Hereditary orotic aciduria and other disorders of pyrimidine

      metabolism.  In The Metabolic and Molecular Bases of Inherited

      Disease. 8th edition. Edited by CR Scriver, AL Beaudet, WS Sly, et al.

      McGraw-Hill Book Company, 2001, pp 2663-2702

Key