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Phenylalanine and Tyrosine
Test Code26336
CPT Codes
84030, 84510
Preferred Specimen
0.4 mL plasma collected in a sodium heparin (green-top) tube
Patient Preparation
Collect specimen after an overnight fast (or at least 4 hrs after a meal) if possible. Non-fasting samples are acceptable for pediatric patients.
Minimum Volume
0.2 mL
Other Acceptable Specimens
Plasma collected in: EDTA (lavender-top) or lithium heparin (green-top) tube • Serum collected in a red-top tube (no gel)
Instructions
Separate plasma from cells as soon as possible and freeze below -20°C.
Date of Collection and Age of the patient must be provided for interpretation and for age related reference ranges to print on the final report.
Date of Collection and Age of the patient must be provided for interpretation and for age related reference ranges to print on the final report.
Transport Temperature
Frozen
Specimen Stability
Room temperature: Unacceptable
Refrigerated: 7 days
Frozen: 30 days
Refrigerated: 7 days
Frozen: 30 days
Methodology
Chromatography/Mass Spectrometry
FDA Status
This test was developed and its analytical performance characteristics have been determined by Quest Diagnostics. It has not been cleared or approved by FDA. This assay has been validated pursuant to the CLIA regulations and is used for clinical purposes.
Setup Schedule
A.M. Sets up 2 days a week.
Limitations
If non-PKU types of hyperphenylalanemia are suspected, additional testing for tetraahydrobiopterin pathway enzyme defects should be performed.
Clinical Significance
Phenylalanine and Tyrosine are used in the monitoring of patients with phenylketonuria (PKU) who are on special diets. Tyrosine analysis can also be used for monitoring of patients with tyrosinemia.
