Use

This assay measures the levels of phenylacetylglutamine (PAG) and its upstream metabolites phenylbutyrate and phenylacetate in plasma. A hallmark of most urea cycle disorders (UCDs) is the toxic accumulation of ammonia that ultimately leads to several 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). Once consumed, both SPB and GPB are converted to phenylacetate, a compound that scavenges ammonia through the formation of PAG. The key to successful treatment of UCDs is the accurate monitoring of patient compliance and ammonia removal. Unfortunately, daily plasma ammonia levels can fluctuate significantly, making them an inexact diagnostic value. Therefore, the urinary excretion of PAG has been proposed as a dosing biomarker, based on the strong correlation between its levels and daily intake of phenylbutyrate.