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

Reporting Name

Amino Acid, Urea Cycle Panel, P

Useful For

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

Clinical Information

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, as ammonia levels rise, present during the neonatal period 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 stressors. 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 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 UCD are inherited autosomal recessively, with the exception of OTC deficiency, which is X-linked. UCD may be suspected in cases 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.


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.

Report Available

3 to 5 days

Day(s) Performed

Monday through Friday

Clinical Reference

1. Brusilow SW, Horwich AL. Urea cycle enzymes. In: Valle DL, Antonarakis S, Ballabio A, Beaudet AL, Mitchell GA. eds. The Online Metabolic and Molecular Bases of Inherited Disease. McGraw Hill; 2019. Accessed October 5, 2022.

2. Haberle J, Burlina A, Chakrapani A, et al: Suggested guidelines for diagnosis and management of urea cycle disorders: First revision. J Inherit Metab Dis. 2019 Nov;42(6):1192-1230. doi: 10.1002/jimd.12100

3. Valle D, Simell O. The Hyperornithinemias. In: Valle DL, Antonarakis S, Ballabio A, Beaudet AL, Mitchell GA. eds. The Online Metabolic and Molecular Bases of Inherited Disease. McGraw Hill; 2019. Accessed October 5, 2022.

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. doi: 10.3748/wjg.v21.i13.4063

5. Ah Mew N, Simpson KL, Gropman AL, et al: Urea cycle disorders overview. In: Adam MP, Ardinger HH, Pagon RA, et al. GeneReviews[Internet]. University of Washington, Seattle; 2003. Updated June 22, 2017. Accessed October 5, 2022. Available at

Method Name

Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS)

Specimen Type


Necessary Information

1. Patient's age is required.

2. Include family history, clinical condition (asymptomatic or acute episode), diet, and drug therapy information.

Specimen Required

Patient Preparation: Fasting (overnight preferred, 4 hours minimum). Infants should be drawn just before next feeding (2-3 hours without total parenteral nutrition if possible).

Collection Container/Tube:

Preferred: Green top (sodium heparin)

Acceptable: Lavender top (EDTA), plasma gel tube, or green top (lithium heparin)

Submission Container/Tube: Plastic vial

Specimen Volume: 0.5 mL

Collection Instructions:

1. Collect specimen and place on wet ice. Note: Thrombin-activated tubes should not be used for collection.

2. Centrifuge immediately or within 4 hours of collection if the specimen is kept at refrigerated temperature.

3. Being careful to ensure that no buffy coat is transferred, aliquot plasma into a plastic vial and freeze.

Specimen Minimum Volume

0.3 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Plasma Frozen 14 days

Reference Values


≤23 months: 316-1020 nmol/mL

2-17 years: 329-976 nmol/mL

≥18 years: 371-957 nmol/mL



≤23 months: 20-130 nmol/mL

2-17 years: 22-97 nmol/mL

≥18 years: 38-130 nmol/mL



≤23 months: 9-38 nmol/mL

2-17 years: 11-45 nmol/mL

≥18 years: 17-46 nmol/mL



≤23 months: 29-134 nmol/mL

2-17 years: 31-132 nmol/mL

≥18 years: 32-120 nmol/mL



<2 nmol/mL


Reference value applies to all ages.

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 US Food and Drug Administration.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
AAUCD Amino Acid, Urea Cycle Panel, P 100368-0


Result ID Test Result Name Result LOINC Value
32440 Glutamine 20643-3
32441 Citrulline 20640-9
32442 Argininosuccinic Acid 32227-1
32443 Arginine 20637-5
32444 Ornithine 20652-4
32445 Interpretation (AAUCD) 49247-0
Mayo Clinic Laboratories | Endocrinology Catalog Additional Information: