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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

Specimen Type

Plasma


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


Collection Container/Tube:

Preferred: Green top (sodium heparin)

Acceptable: EDTA or green top (lithium heparin)

Submission Container/Tube: Plastic vial

Specimen Volume: 0.5 mL

Collection Instructions:

1. Fasting (overnight preferred, 4 hours minimum). Infants should be drawn just before next feeding (2-3 hours without TPN if possible).

2. Centrifuge within 4 hours if specimen is stored at refrigerated temperature and aliquot plasma. Send plasma frozen.


Specimen Minimum Volume

0.25 mL

Specimen Stability Information

Specimen Type Temperature Time
Plasma Frozen 14 days

Reference Values

GLUTAMINE

≤23 months: 316-1020 nmol/mL

2-17 years: 329-976 nmol/mL

≥18 years: 371-957 nmol/mL

 

ORNITHINE

≤23 months: 20-130 nmol/mL

2-17 years: 22-97 nmol/mL

≥18 years: 38-130 nmol/mL

 

CITRULLINE

≤23 months: 9-38 nmol/mL

2-17 years: 11-45 nmol/mL

≥18 years: 17-46 nmol/mL

 

ARGININE

≤23 months: 29-134 nmol/mL

2-17 years: 31-132 nmol/mL

≥18 years: 32-120 nmol/mL

 

ARGININOSUCCINIC ACID

<2 nmol/mL

Reference value applies to all ages.

Day(s) and Time(s) Performed

Monday through Friday; 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

82136

LOINC Code Information

Test ID Test Order Name Order LOINC Value
AAUCD Amino Acid, Urea Cycle Panel, P In Process

 

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) 59462-2

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 urea cycle serves to break down 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. Infants with a complete enzyme deficiency typically appear normal at birth, but present 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.

 

All of the UCDs are inherited as autosomal recessive disorders, with the exception of OTC deficiency, which is X-linked. UCDs 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 a UCD. 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 UCDs 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.

Interpretation

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.

Clinical Reference

1. Scriver's The Online Metabolic and Molecular Bases of Inherited Disease (OMMBID). Part 8 Amino Acids. Accessed July 6, 2016. Available at: http://ommbid.mhmedical.com/book.aspx?bookid=971

2. Haberle J, Boddaert N, Burlina A, Chakrapani A, et al: Suggested guidelines for diagnosis and management of urea cycle disorders. Orphanet J Rare Dis 2012;7:32

3. Singh RH: Nutritional management of patients with urea cycle disorders. J Inher Metab Dis 2007;30(6):880-887

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

Analytic Time

3 days (not reported on Saturday or Sunday)

Method Name

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

Mayo Medical Laboratories | Genetics and Pharmacogenomics Catalog Additional Information:

mml-biochemical