Specimen Requirements


Phenylalanine and Tyrosine

Specimen Requirement

Collect Lavender EDTA or lithium heparin, centrifuge as soon as possible, transfer 0.4 mL plasma to a screw top plastic tube, indicate sample type on tube and send refrigerated.

Collect specimen after an overnight fast (or at least 4 hrs after a meal) if possible. Non-fasting samples are acceptable for pediatric patients.


Chromatography/Mass Spectrometry


Room temp: Unacceptable, Refrigerated: 7 days, Frozen: 30 days.

Reference Range

By Report*


4-9 days, Set up: Tuesday and Friday

Clinical Use

Useful for monitoring patients with an established diagnosis of phenylketonuria (PKU and monitoring effectiveness of dietary therapy in patients with hyperphenylalaninemia. Defects in phenylalanine hydroxylase (PAH) cause the majority of cases of hyperphenylalaninemia (HPA); however, approximately 2% of infants with HPA have impaired synthesis or recycling of tetrahydrobiopterin (BH4).

Test Code