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Test Code LAB5336 Phenylalanine (PKU), Quantitative, Blood

Performing Laboratory

St. Louis Children's Hospital - Metabolic Genetics

Methodology

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

Reference Values

Reference Range:

<1 month: 30-120 micmol/L
≥ 1 month: 30-90 micmol/L                                                                        

Critical Values: None established

Last Reviewed

07/2025

Sample Rejection

Mislabeled or unlabeled specimens.

Specimen Requirements

Patient Preparation: None

Container/Tube

Preferred: Mint green-top lithium heparin (MNTGRN LiHep) tube

Acceptable: green SAMPLETTE/MICROTAINER, Plain Red-top tube, Gold SST gel tube or Dark Green-top (NaHep) tube

Collection Volume: 2.0 mL (minimum 0.5 mL)

Submission container/tube: If specimen is coming from outside facility, process specimen within 1 hour. Aliquot plasma/serum into a screw cap plastic vial for transport (labeling aliquot with specimen type) and freeze. Send on dry ice to keep frozen

Special Instructions: Send to lab promptly.

Additional Information

For SLCH Laboratory use only

Lab Processing instructions: Centrifuge specimen to separate and aliquot sample into a plastic conical tube (label as serum if collected in Red top or gold SST gel tube). Place aliquot tube in freezer. (see note below)

Processed Volume: 0.3 mL plasma/serum

Analyte Stability:

Specimen Type Temperature Time
Whole Blood (unprocessed)  Ambient 5 days
Plasma/Serum (processed)    Refrigerated     1 week
  Ambient  5 days
  Frozen (preferred)    indefinitely  

Notes: Specimens coming from outside facilities that are in aliquot containers should be kept in original container sent when given to Met. Genetics lab (put in freezer).

Test Classification and CPT Code

84030
Test Classification: This test was developed and its performance characteristics determined by St. Louis Children's Hospital Clinical Laboratory. It has not been cleared or approved by the U.S. Food and Drug Administration.

Logistics

Test Availability: Daily

Days set up: Monday-Friday

Cut-off time: Varies; batched once per day in a.m.
Turnaround Time: 24-72 hours
 

LOINC

14875-9

Limitations

  • NA