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HelpTest Code LAB1913 Phenylalanine and Tyrosine, Plasma
Additional Codes
PKU
Useful For
Monitoring effectiveness of dietary therapy in patients with hyperphenylalaninemia
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Specimen Type
PlasmaNecessary Information
1. Patient's age is required.
2. Include family history, clinical condition (asymptomatic or acute episode), diet, and drug therapy information.
Specimen Required
Patient Preparation: Patient should fast overnight (8-12 hour fast); infants should have specimen collected before next feeding (4 hour fast)
Collection Container/Tube:
Preferred: Green top (Sodium heparin)
Acceptable: Green top (Lithium heparin), lavender top (EDTA)
Submission Container/Tube: Plastic vial
Specimen Volume: 0.5 mL
Collection Instructions:
1. Centrifuge and aliquot plasma into a plastic vial.
2. Send plasma frozen.
Specimen Minimum Volume
0.1 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Plasma | Frozen (preferred) | 14 days | |
| Refrigerated | 14 days |
On-campus collections: Tube to 99 or deliver to University Extension Hospital Room EH318
Submission Container/Tube: Plastic vial, Frozen
Off-campus collections:
Centrifuge and aliquot within 2 hours.
Specimen to be stored/transported Frozen
Reference Values
PHENYLALANINE
Premature: 98-213 nmol/mL
0-31 days: 38-137 nmol/mL
1-24 months: 31-75 nmol/mL
2-18 years: 26-91 nmol/mL
≥19 years: 35-85 nmol/mL
Conversion Formulas:
Result in mg/dL x 60.5=result in nmol/mL
Result in nmol/mL x 0.0165=result in mg/dL
TYROSINE
Premature: 147-420 nmol/mL
0-31 days: 55-147 nmol/mL
1-24 months: 22-108 nmol/mL
2-18 years: 24-115 nmol/mL
≥19 years: 34-112 nmol/mL
Conversion Formulas:
Result in mg/dL x 55.2=result in nmol/mL
Result in nmol/mL x 0.0181=result in mg/dL
Day(s) Performed
Monday through Friday
CPT Code Information
84030 Phenylalanine
84510 Tyrosine
82542 (if appropriate for government payers)
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| PKU | Phenylalanine and Tyrosine, P | 101402-6 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 8380 | Phenylalanine, P | 14875-9 |
| 8627 | Tyrosine, P | 20660-7 |
Interpretation
The quantitative results of phenylalanine and tyrosine with age-dependent reference values are reported without added interpretation. When applicable, reports of abnormal results may contain an interpretation based on available clinical interpretation.
A phenylalanine:tyrosine ratio higher than 3 is considered abnormal.
Method Description
This method quantifies phenylalanine (Phe) and tyrosine (Tyr) using stable isotope-labeled internal standards (IS): d5-Phe and d4-Tyr. Phe and Tyr are extracted from plasma. The supernatant is diluted and then introduced into the tandem mass spectrometer. The concentration of Phe and Tyr are established by comparison of the ion intensity with that of the IS.(Unpublished Mayo method)
Report Available
2 to 4 daysSpecimen Retention Time
2 weeksReject Due To
| Gross hemolysis | OK |
| Gross lipemia | OK |
| Gross icterus | OK |
Method Name
Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS)
Forms
If not ordering electronically, complete, print, and send a Biochemical Genetics Test Request (T798) with the specimen.