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Phenylalanine

Phenylalanine Monitoring, Plasma

Test Codes

ARUP: 80315, Order as a Miscellaneous Send Out (LAB6433).

Department

Send Outs

Specimen Collection Criteria

Collect: One Dark Green-top Lithium or Sodium Heparin tube.

Send specimen for processing immediately after collection.

Physician Office/Draw Specimen Preparation

Centrifuge to separate plasma from cells within two hours of collection. Transfer plasma to a plastic transport tube and freeze (-20°C/-4°F or below) immediately.

Preparation for Courier Transport

Transport: 0.5 mL plasma, frozen (-20°C/-4°F or below). (Minimum: 0.25 mL)

Rejection Criteria

• Hemolyzed specimens.
• Specimens not collected and processed as indicated.

In-Lab Processing

Centrifuge to separate plasma from cells within two hours of collection. Transfer plasma to a plastic transport tube and freeze (-20°C/-4°F or below) immediately.

Transport: 0.5 mL plasma, frozen (-20°C/-4°F or below). (Minimum: 0.25 mL)

Storage

Specimen Stability for Testing:

Room Temperature (20-26°C or 68-78.8°F): Unacceptable
Refrigerated (2-8°C or 36-46°F): 24 hours
Frozen (-20°C/-4°F or below): 1 month

Specimen Storage in Department Prior to Disposal:

Specimen retention time is determined by the policy of the reference laboratory. Contact the Send Outs Laboratory with any questions.

Laboratory

Sent to ARUP Laboratories, Salt Lake City, UT.

Performed

Monday – Friday.
Results available in 3-6 days.

Reference Range

0-30 days: 30-100 mcmol/L.
1 month - 11 months: 30-90 mcmol/L.
Greater than 1 year: 30-80 mcmol/L.

Test Methodology

Quantitative Liquid Chromatography / Tandem Mass Spectrometry.

Interpretation

Increased levels of plasma phenylalanine may occur in primary hyperphenylalaninemias, sepsis, severe burns, transient tyrosinemia of the newborn, transient hyperphenylalaninemia of the newborn, viral hepatitis or hepatic encephalopathy. Until proven otherwise, hyperphenylalaninemia in a neonate implies a disorder of phenylalanine hydroxylation. This is usually caused by a deficiency in phenylalanine hydroxylase, but may be caused by tetrahydrobiopterin (BH₄) deficiency and defects in BH₄ synthesis.

Clinical Utility

The phenylalanine assay is used for the quantitative confirmation of abnormal values obtained from mandated state screening programs for the detection of phenylketonuria (PKU) caused by a deficiency of phenylalanine hydroxylase. It is also used to monitor patients being treated for phenylalanine disorders.

CPT Codes

82131

Contacts

Last Updated

11/3/2023