Casandra

Casandra Test Code MC76354Version 1 (DRAFT)

Performing Lab

Lab Mayo Clinic LabLab Test ID PKUBSCPT Codes 82542, 84030, 84510

Phenylalanine and Tyrosine, Blood Spot

Clinical Use

Use

This test is used for monitoring the effectiveness of therapy in patients with hyperphenylalaninemia. It is not sufficient for follow-up for abnormal newborn screening results or for establishing a diagnosis of a specific cause of hyperphenylalaninemia. Phenylketonuria (PKU) is the most frequent inherited disorder of amino acid metabolism, and its proper management includes monitoring phenylalanine and tyrosine levels. Patients with hyperphenylalaninemia need to be evaluated for adequate dietary management, and the phenylalanine:tyrosine ratio is crucial in assessing dietary intake.

Special Instructions

Not provided.

Limitations

This test does not provide sufficient follow-up for abnormal newborn screening results because other causes of hyperphenylalaninemia (such as tetrahydrobiopterin deficiency) cannot be excluded by this test alone. It is not useful for diagnosing the specific cause of hyperphenylalaninemia. Conditions that might result in specimen rejection include blood spot specimens that show serum rings or have multiple layers and insufficient specimen volume. Additionally, unapproved filter papers can cause specimen rejection.

Test Details

New York Approved

Methodology

Mass Spectrometry (LC-MS/MS)

Biomarkers

Phenylalanine

Analyte

Phenylalanine, BS

Concentration / Level • Quantitative (Continuous) (e.g., copies/mL, % expression)

Tyrosine

Analyte

Tyrosine, BS

Concentration / Level • Quantitative (Continuous) (e.g., copies/mL, % expression)

LOINC Codes

Order Codes

79621-9 - Phe + Tyr Pnl DBS

Result Codes

29573-3 - Phe DBS-sCnc
35571-9 - Tyrosine DBS-sCnc
18771-6 - Provider signing name

Result Turnaround Time

3-5 days

Specimen

Dried Blood Spot

Volume

2 Blood spots

Minimum Volume

1 Blood spot

Container

Blood Spot Collection Card

Collection Instructions

An alternative blood collection option for a patient older than 1 year is a fingerstick. Let blood dry on filter paper at room temperature in a horizontal position for a minimum of 3 hours. Do not expose specimen to heat or direct sunlight. Do not stack wet specimens. Keep specimen dry.

Causes for Rejection

Blood spot specimen that shows serum rings or has multiple layers; insufficient specimen; unapproved filter papers

Stability Requirements

Temperature	Period
Room Temperature	90 days
Refrigerated	90 days
Frozen	90 days

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