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Genetic Labs

Houston, Texas

Genetic Laboratory
Baylor Genetics Laboratories
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Medical Genetics Test Details

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Phenylbutyrate Metabolite Analysis
Test Information: This assay measures the levels of phenylacetylglutamine (PAG) and its upstream metabolites phenylbutyrate and phenylacetate in plasma.
Test Details
Test Code: 4650
Special Notes: This test can also be performed on Urine (#4651) or Cerebrospinal Fluid (#4652).


A hallmark of most urea cycle disorders (UCDs) is the toxic accumulation of ammonia that ultimately leads to a number of clinical features, including cognitive impairment. Accordingly, treatment for UCD patients involves daily oral intake of ammonia scavenging drugs, including sodium phenylbutyrate (SPB) and/or glycerol phenylbutyrate (GPB) which go by the trade names BUPHENYLŪ and RAVICITIŪ, respectively. Once consumed, both SPB and GPB are converted to phenylacetate, a compound that scavenges ammonia through the formation of the urine excreted metabolite phenylacetylglutamine (PAG) (1-3). Sodium phenylbutyrate is also in phase I clinical trials for the treatment of Parkinson disease to slow progression of disease and to reduce death of dopaminergic neurons (4, 5).

Key to successful treatment of UCDs is the accurate monitoring of patient compliance and ammonia removal. Unfortunately, even under optimal conditions, a patient?s daily plasma ammonia levels can fluctuate by as much as 10-fold, rendering it an inexact diagnostic value for clinical management (2, 3). Instead, urinary excretion of PAG has been proposed as a dosing biomarker based on the strong correlation between urine excreted PAG and daily intake of phenylbutyrate (3). To allow comprehensive monitoring of UCD patients, our assays measure urine, plasma, and CSF levels of PAG and its upstream precursors phenylbutyrate and phenylacetate.

1. Lee B, et al. (2010) Phase 2 comparison of a novel ammonia scavenging agent with sodium phenylbutyrate in patients with urea cycle disorders: safety, pharmacokinetics and ammonia control. Molecular genetics and metabolism 100(3):221-228.
2. Lichter-Konecki U, et al. (2011) Ammonia control in children with urea cycle disorders (UCDs); phase 2 comparison of sodium phenylbutyrate and glycerol phenylbutyrate. Molecular genetics and metabolism 103(4):323-329.
3. Mokhtarani M, et al. (2012) Urinary phenylacetylglutamine as dosing biomarker for patients with urea cycle disorders. Molecular genetics and metabolism 107(3):308-314.
4. Roy A, et al. (2012) Sodium phenylbutyrate controls neuroinflammatory and antioxidant activities and protects dopaminergic neurons in mouse models of Parkinson's disease. PloS one 7(6):e38113.
5. Zhou W, et al. (2011) Phenylbutyrate up-regulates the DJ-1 protein and protects neurons in cell culture and in animal models of Parkinson disease. The Journal of biological chemistry 286(17):14941-14951.

Related Tests:
Plasma Amino Acids (#4100)
Urine Orotic Acid (#4210)
Technical Information
Test Type: Analyte Analysis
Sample & Shipping Information
Test Requisition: Biochemical
Specimen Type: Plasma
Requirements: Draw blood in a Sodium Heparin (green-top) tube(s) and separate as soon as possible. Send 1-2 cc of plasma. Store the specimen frozen at -20C. Specimen may be stored frozen for up to 7 days.
Shipping Conditions: Ship frozen on 3-5 lbs of dry ice in an insulated container by overnight courier.

Turn Around Time: 8 days
Billing Information
List Price: *For Insurance or Institutional Prices, please call.
CPT Codes: 82542x1, 83789x1

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