Urea Cycle Disorder (UCD) Testing
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Urea Cycle Disorder Genetic Testing

Genetic testing may identify affected enzymes that can cause a urea cycle disorder (UCD). A blood, saliva, or buccal sample is taken and sent to a laboratory where the patient’s DNA is analyzed to identify a defective gene.

Genetic testing and counseling are vital to optimizing patient outcomes by assisting in assessing risk, diagnosing family members, and helping inform disease management decisions.1-3 Identifying affected family members prior to disease presentation allows measures to be taken to prevent hyperammonemia.3

Although genetic testing is important, identifying UCDs in newborns can be challenging. Newborn screening tests for UCDs vary state to state, and not all UCD subtypes have a newborn screening test.3 While ornithine transcarbamylase (OTC) deficiency is the most common UCD subtype, it is only screened for in Connecticut, Kentucky, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont.3,4

Genetic testing can help you and your patient understand
the cause of a UCD

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Monitoring Urea Cycle Disorder Lab Tests

Patients with a UCD require regular monitoring of their labs because their ammonia levels may become dangerously high.5,6 Measuring ammonia, however, can be challenging and may result in a false elevated ammonia level if blood is not drawn correctly.6,7

Careful collection and processing can help ensure reliability of results.7 Consider the following guidance7,8:

  • Collect free-flowing venous or arterial blood
  • Ensure the patient is relaxed as stress can cause spurious increases in ammonia levels
  • Draw blood into a pre-chilled vacuum tube and place it on ice for transport
  • At the laboratory, blood should be separated within 15 minutes and analyzed immediately

Learn Correct Procedures for Accurate Ammonia Testing

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In addition to ammonia, glutamine can be used as an indicator of metabolic control in patients with a UCD.3,9 Phenylbutyrate metabolite testing may also be used in conjunction with ammonia and glutamine levels to help guide management decisions and optimize treatment.10-12 Additional labs may be appropriate for each unique patient and UCD subtype.

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References: 1. Fujisawa D, Mitsubuchi H, Matsumoto S, et al. Early intervention for late-onset ornithine transcarbamylase deficiency. Pediatr Int. 2015;57(1):e1-e3. doi:10.1111/ped.12457 2. National Organization for Rare Disorders (NORD). The Physician’s Guide to Urea Cycle Disorders. Accessed March 23, 2020. https://rarediseases.org/physician-guide/urea-cycle-disorders/ 3. Ah Mew N, Simpson KL, Gropman AL, Lanpher BC, Chapman KA, Summar ML. Urea Cycle Disorders Overview. In: Adam MP, Mirzaa GM, Pagon RA, et al., eds. GeneReviews®. Seattle (WA): University of Washington, Seattle; April 29, 2003. 4. Lichter-Konecki U, Caldovic L, Morizono H, et al. Ornithine Transcarbamylase Deficiency. 2013 Aug 29 [Updated 2016 Apr 14]. In: Adam MP, Ardinger HH, Pagon RA, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2019. 5. Pei KJ, Pei KJ, Rajikan RB, et al. Growth and nutritional status of children with urea cycle defects (UCD): a 6-months follow up study in Institute of Pediatric, Hospital Kuala Lumpur. Int J Clin Nutr. 2014; 2(3):41-52. doi:10.12691/ijcn-2-3-1 6. Häberle J, Boddaert N, Burlina A, et al. Suggested guidelines for the diagnosis and management of urea cycle disorders. Orphanet J Rare Dis. 2012;7:32. Published 2012 May 29. doi:10.1186/1750-1172-7-32 7. Barsotti RJ. Measurement of ammonia in blood. J Pediatr. 2001;138(1 Suppl):S11-S20. doi:10.1067/mpd.2001.111832 8. Hawke L. Ammonia (Plasma, Blood). Association of Clinical Biochemistry; 2012. 9. Lee B, Diaz GA, Rhead W, et al. Glutamine and hyperammonemic crises in patients with urea cycle disorders. Mol Genet Metab. 2016;117(1):27-32. doi:10.1016/j.ymgme.2015.11.005 10. Mokhtarani M, Diaz GA, Rhead W, et al. Elevated phenylacetic acid levels do not correlate with adverse events in patients with urea cycle disorders or hepatic encephalopathy and can be predicted based on the plasma PAA to PAGN ratio. Mol Genet Metab. 2013;110(4):446-453. doi:10.1016/j.ymgme.2013.09.017 11. Mokhtarani M, Diaz GA, Rhead W, et al. Urinary phenylacetylglutamine as dosing biomarker for patients with urea cycle disorders. Mol Genet Metab. 2012;107(3):308-314. doi:10.1016/j.ymgme.2012.08.006 12. Häberle J, Burlina A, Chakrapani A, et al. Suggested guidelines for the diagnosis and management of urea cycle disorders: First revision. J Inherit Metab Dis. 2019;42(6):1192-1230. doi:10.1002/jimd.12100