Phenylalanine and Tyrosine
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.
Room temp: Unacceptable, Refrigerated: 7 days, Frozen: 30 days.
4-9 days, Set up: Tuesday and Friday
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).