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Order Code PKUBS Phenylalanine and Tyrosine, Blood Spot


Ordering Guidance


For follow-up of an abnormal newborn screen for potential phenylketonuria, order PKU / Phenylalanine and Tyrosine, Plasma.

Necessary Information


Patient's age is required.



Specimen Required


Submit only 1 of the following specimen types:

 

Preferred:

Specimen Type: Blood spot

Supplies: Card-Blood Spot Collection (Filter Paper) (T493)

Container/Tube:

Preferred: Blood Spot Collection Card

Acceptable: Whatman Protein Saver 903 Paper, PerkinElmer 226 filter paper, Munktell filter paper, or blood collected in tubes containing EDTA and dried on filter paper.

Specimen Volume: 2 Blood spots

Collection Instructions:

1. An alternative blood collection option for a patient older than 1 year is a fingerstick. For detailed instructions, see How to Collect Dried Blood Spot Samples.

3. Let blood dry on filter paper at room temperature in a horizontal position for a minimum of 3hours.

4. Do not expose specimen to heat or direct sunlight.

5. Do not stack wet specimens.

6. Keep specimen dry.

Specimen Stability Information: Ambient (preferred) 90 days/Refrigerated 90 days/Frozen 90 days

Additional Information:

1. For collection instructions, see Blood Spot Collection Instructions

2. For collection instructions in Spanish, see Blood Spot Collection Card-Spanish Instructions (T777

3. For collection instructions in Chinese, see Blood Spot Collection Card-Chinese Instructions (T800)

 

Acceptable:

Specimen Type: Whole blood

Container/Tube: Lavender top (EDTA)

Specimen Volume: 2 mL

Collection Instructions: Send whole blood specimen in original tube. Do not aliquot.

Specimen Stability Information: Refrigerate 6 days


Useful For

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

Genetics Test Information

This test provides evaluation of patients with hyperphenylalaninemia or monitoring effectiveness of therapy.

 

This test does not provide sufficient follow-up for abnormal newborn screening results because other causes of hyperphenylalaninemia (eg, tetrahydrobiopterin deficiency) cannot be excluded by this test alone.

Method Name

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

Reporting Name

Phenylalanine and Tyrosine, BS

Specimen Type

Whole blood

Specimen Minimum Volume

Blood spots: 1
Whole blood: 0.5 mL

Specimen Stability Information

Specimen Type Temperature Time
Whole blood Varies

Reject Due To

Blood spot specimen that shows serum rings or has multiple layers Reject
Insufficient specimen Reject
Unapproved filter papers Reject

Reference Values

PHENYLALANINE

27-107 nmol/mL

 

TYROSINE

<4 weeks: 40-280 nmol/mL

≥4 weeks: 25-150 nmol/mL

Method Description

A 3-mm disk is punched out of the dried blood spot onto a 96-well plate. The amino acids are extracted by the addition of acetonitrile and known concentrations of isotopically labeled amino acids as internal standards. The extract is moved to another 96-well plate, dried under a stream of nitrogen, and derivatized by the addition of n-butanol hydrochloric acid. Analytes are measured by liquid chromatography tandem mass spectrometry. The concentrations of the phenylalanine and tyrosine are established by computerized comparison of ion intensities of these analytes to that of the respective internal standards.(Unpublished Mayo method)

Day(s) Performed

Monday through Friday

Performing Laboratory

Mayo Clinic Laboratories in Rochester

CPT Code Information

84030

84510

82542 (if appropriate for government payers)