This test is designed to detect carriers of phenylketonuria. Phenylketonuria (PKU) is an autosomal recessive disorder resulting from faulty metabolism of the amino acid, phenylalanine. In individuals with untreated PKU, dietary intake of phenylalanine can lead to profound intellectual disability, behavioral issues, epilepsy, hypopigmentation, and a musty body odor. Additionally, women with PKU are at risk for having children with various birth defects due to exposure of the baby to high phenylalanine levels from maternal plasma. Newborn screening and early initiation of treatment, including lifelong dietary restriction of phenylalanine, can significantly improve disease prognosis. PKU (MIM 261600) is caused by pathogenic variants in the PAH gene (NM_000277). Individuals with a heterozygous pathogenic PAH variant are carriers for PKU and are at risk of having a child with this disorder. If both reproductive partners are PKU carriers, the risk for PKU in their children is 25%. The prevalence of PKU varies in different populations and is more common in individuals of Turkish, Irish, northern European, and East Asian ancestry. This test is intended for pre/post-conception carrier screening and is not intended for diagnostic testing.