Phenylalanine and Tyrosine PHENYLAL

Synonyms

Allscripts (AEHR) Order Name

Phenylalanine and Tyrosine

Sunrise Clinical Manager (SCM) Order Name

Phenylalanine/Tyrosine Ratio Measurement

Clinical Info

Monitoring effectiveness of therapy in patients with hyperphenylalaninemia

This test is not sufficient for follow-up for abnormal newborn screening results or for establishing a diagnosis of a specific cause of hyperphenylalaninemia.

Specimen Type

Blood

Container

Lavender Top Tube

Collection Instructions

Container/Tube: Dark Green top (sodium heparin) or Lavender (EDTA Top Tube
Specimen: 2.0 mL (minimum volume: 0.5 mL) of whole blood Send original rube do not aliquot
Transport Temperature: Room Temperature

Alternate:
Blood Spot Card 2 spots Protect from Light

Transport Instructions

Refrigerated

Specimen Stability

Whole Blood
4 Days Room Temperature or Refrigerated

Methodology

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

Days Performed

Monday through Friday
TAT: 4-6 Days

Performing Laboratory

Mayo Medical Labroratories

CPT

84030-Phenylalanine
84510-Tyrosine
LONIC Code: 79621-9

PDM

5302878

Result Interpretation

PHENYLALANINE            27.0-107.0 nmol/mL

 

TYROSINE

                         <4 weeks: 40.0-280.0 nmol/mL

                  > or =4 weeks: 25.0-150.0 nmol/mL

 

 

The quantitative results of phenylalanine and tyrosine with

age-dependent reference values are reported without added

interpretation. When applicable, reports of abnormal results

may contain an interpretation based on available clinical information.

 

 A phenylalanine:tyrosine ratio higher than 3 is considered abnormal.

Phenylketonuria (PKU) is the most frequent inherited disorder of amino acid metabolism (about 1:10,000-1:15,000) and was the first successfully treated inborn error of metabolism. It is inherited in an autosomal recessive manner and is caused by a defect in the enzyme phenylalanine hydroxylase (PAH), which converts the essential amino acid phenylalanine to tyrosine. Deficiency of PAH results in decreased levels of tyrosine and an accumulation of phenylalanine in blood and tissues. Untreated, PKU leads to severe brain damage with intellectual impairment, behavior abnormalities, seizures, and spasticity. The level of enzyme activity differentiates classic PKU (PAH activity <1%) from other milder forms; however, all are characterized by increased levels of phenylalanine (hyperphenylalaninemia). Treatment includes the early introduction of a diet low in phenylalanine. Some patients may also benefit from adjuvant tetrahydrobiopterin (BH4) supplementation (a cofactor for PAH), or enzyme substitution therapy.

Forms

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