PKU - Overview: Phenylalanine and Tyrosine, Plasma

Test Catalog

Test Name

Test ID: PKU    
Phenylalanine and Tyrosine, Plasma

Useful For Suggests clinical disorders or settings where the test may be helpful

Monitoring effectiveness of dietary therapy in patients with hyperphenylalaninemia

Genetics Test Information Provides information that may help with selection of the correct test or proper submission of the test request

Phenylketonuria: Evaluation of patients with hyperphenylalaninemia or monitoring effectiveness of dietary therapy. Not sufficient follow-up for abnormal newborn screening results, because other causes of hyperphenylalaninemia (eg, BH4 deficiency) cannot be excluded by this test alone.

Tyrosinemia, type I: For medical management.


Defects in phenylalanine hydroxylase (PAH) cause the majority of cases of hyperphenylalanemia (HPA); however, approximately 2% of infants with HPA have impaired synthesis or recycling of tetrahydrobiopterin (BH4).


Measurement of phenylalanine and tyrosine is not sufficient to establish a diagnosis of phenylketonuria (PKU) because other forms of HPA are not excluded by this test.

Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test

Method Name A short description of the method used to perform the test

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

NY State Approved Indicates the status of NY State approval and if the test is orderable for NY State clients.


Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name

Phenylalanine and Tyrosine, P

Aliases Lists additional common names for a test, as an aid in searching

Phenylalanine Includes Tyrosine
PKU (Phenylketonuria)