Test Catalog

Test ID: AAUCD    
Amino Acids, Urea Cycle Disorders Panel, Plasma

Useful For Suggests clinical disorders or settings where the test may be helpful

Differential diagnosis and follow-up of patients with urea cycle disorders

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Urea cycle disorders (UCD) are a group of inherited disorders of nitrogen detoxification that result when any of the enzymes in the urea cycle (carbamoylphosphate synthetase I: CPS I; ornithine transcarbamylase: OTC; argininosuccinic acid synthetase; argininosuccinic acid lyase; arginase; or the cofactor producer, N-acetyl glutamate synthetase: NAGS), have deficient or reduced activity. The role of the urea cycle is to metabolize and clear waste nitrogen, and defects in any of the steps of the pathway can result in an accumulation of ammonia, which can be toxic to the nervous system. The urea cycle is also responsible for endogenous production of the amino acids citrulline, ornithine, and arginine. Infants with a complete urea cycle enzyme deficiency typically appear normal at birth, but present with in the neonatal period as ammonia levels rise with lethargy, seizures, hyper- or hypoventilation, and ultimately coma or death. Individuals with partial enzyme deficiency may present later in life, typically following an acute illness or other stressor. Symptoms may be less severe and may present with episodes of psychosis, lethargy, cyclical vomiting, and behavioral abnormalities. Patients with impaired ornithine metabolism due to ornithine aminotransferase (OAT) deficiency may present with childhood onset myopia progressing to vision loss in the 4th to 6th decades of life. Patients may or may not have accompanying hyperammonemia, but display marked elevations in plasma ornithine.


All of the UCD are inherited as autosomal recessive disorders, with the exception of OTC deficiency, which is X-linked. UCD may be suspected with elevated ammonia, normal anion gap, and a normal glucose. Plasma amino acids can be used to aid in the diagnosis of UCD and may aid in monitoring treatment effectiveness. Measurement of urinary orotic acid, enzyme activity (CPS I, OTC, or NAGS), and molecular genetic testing can help to distinguish the conditions and allows for diagnostic confirmation.


Acute treatment for UCD consists of dialysis and administration of nitrogen scavenger drugs to reduce ammonia concentration. Chronic management typically involves restriction of dietary protein with essential amino acid supplementation. More recently, orthotopic liver transplantation has been used with success in treating some patients.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.


< or =23 months: 316-1020 nmol/mL

2-17 years: 329-976 nmol/mL

> or =18 years: 371-957 nmol/mL



< or =23 months: 20-130 nmol/mL

2-17 years: 22-97 nmol/mL

> or =18 years: 38-130 nmol/mL



< or =23 months: 9-38 nmol/mL

2-17 years: 11-45 nmol/mL

> or =18 years: 17-46 nmol/mL



< or =23 months: 29-134 nmol/mL

2-17 years: 31-132 nmol/mL

> or =18 years: 32-120 nmol/mL



<2 nmol/mL

Reference value applies to all ages.

Interpretation Provides information to assist in interpretation of the test results

The quantitative results of glutamine, ornithine, citrulline, arginine, and argininosuccinic acid with age-dependent reference values are reported without added interpretation. When applicable, reports of abnormal results may contain an interpretation based on available clinical interpretation.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Reference values are for fasting patients.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Brusilow SW, Horwich AL: Brusilow S.W., Horwich A.L. Brusilow, Saul W., and Arthur L. Horwich.Urea Cycle Enzymes. In The Online Metabolic and Molecular Bases of Inherited Disease. Edited by D Valle, AL Beaudet, B Vogelstein, et al. New York, McGraw-Hill, 2014. Accessed May 28, 2019. Available at http://ommbid.mhmedical.com/content.aspx?bookid=971&sectionid=62674945

2. Haberle J, Burlina A, Chakrapani A, et al: Suggested guidelines for diagnosis and management of urea cycle disorders: First revision. OJ Inherit Metab Dis 2019;1-39 doi.org/10.1002/jimd.12100

3. Valle D, Simell O: Valle D, Simell O Valle, David, and Olli Simell.The Hyperornithinemias. In The Online Metabolic and Molecular Bases of Inherited Disease. Edited by D Valle, AL Beaudet, B Vogelstein, et al. New York, McGraw-Hill; 2014. Accessed May 28, 2019. Available at http://ommbid.mhmedical.com/content.aspx?bookid=971&sectionid=62674636.

4. Foshci FG, Morelli MC, Savini S, et al: Urea cycle disorders: A case report of a successful liver transplant and a literature review. World J Gastroenterol 2015 Apr 7;21(13):4063-4068

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, 1993-2019. 2003 Apr 29. Retrieved May 28, 2019. Available at https://www.ncbi.nlm.nih.gov/books/NBK1217/