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Test ID 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:



Specimen Type: Blood spot

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


Preferred: Blood Spot Collection Card

Acceptable: Whatman Protein Saver 903 Paper, PerkinElmer 226 (formerly Ahlstrom 226) filter paper, Munktell filter paper, or blood collected in tubes containing heparin, ACD or 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 of age is a fingerstick. See Dried Blood Spot Collection Tutorial for how to collect blood spots via fingerstick.

2. At least 2 spots should be complete (ie, unpunched).

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)



Specimen Type: Whole blood


Preferred: Lavender top (EDTA)

Acceptable: Green top (sodium or lithium heparin) and yellow top (ACD)

Specimen Volume: 2 mL

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

Specimen Stability Information: Refrigerate (preferred) 4 days/Ambient 4 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

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 Special Container
Whole blood Varies

Reference Values


27.0-107.0 nmol/mL



<4 weeks: 40.0-280.0 nmol/mL

≥4 weeks: 25.0-150.0 nmol/mL

Day(s) Performed

Monday through Friday

Report Available

3 to 5 days

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Test Classification

This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information



82542 (if appropriate for government payers)

LOINC Code Information

Test ID Test Order Name Order LOINC Value
PKUBS Phenylalanine and Tyrosine, BS 79621-9


Result ID Test Result Name Result LOINC Value
92405 Phenylalanine, BS 29573-3
92406 Tyrosine, BS 35571-9
92407 Reviewed By 18771-6