Phenylalanine and Tyrosine

Test Code

26336

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 hours after a meal) if possible. Non-fasting samples are acceptable for pediatric patients.

Minimum Volume

0.2 mL

Other Acceptable Specimens

Plasma collected in: lithium heparin (green-top) tube, or EDTA (lavender-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 .

Transport Temperature

Frozen

Specimen Stability

Room temperature: Unacceptable
Refrigerated: 7 days
Frozen: 30 days

Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)

Received room temperature

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 the U.S. Food and Drug Administration. This assay has been validated pursuant to the CLIA regulations and is used for clinical purposes.

Setup Schedule

Set up: Tues, Thurs; Report available: 4-9 days

Limitations

If non-PKU types of hyperphenylalanemia are suspected, additional testing for tetraahydrobiopterin pathway enzyme defects should be performed.

Reference Range

⁠⁠⁠⁠⁠⁠⁠Phenylalanine

≤30 days	30-79 umol/L
31 days-23 months	31-92 umol/L
2-17 years	38-86 umol/L
≥18 years	40-74 umol/L

Tyrosine

≤30 days	33-160 umol/L
31 days-23 months	24-125 umol/L
2-17 years	31-108 umol/L
≥18 years	38-96 umol/L

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.

Performing Laboratory

Quest Diagnostics Nichols Institute-San Juan Capistrano, CA

33608 Ortega Highway

San Juan Capistrano, CA 92675-2042

The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.