Skip to content

Phenylalanine/Creatinine Ratio, Urine

Published: August 9, 2026Updated: August 16, 2026

A urine test that measures phenylalanine relative to creatinine. It may be used to assess phenylalanine excretion in people being monitored for phenylketonuria.

Quick summary

["This ratio helps show whether unusually high amounts of phenylalanine are being lost in the urine."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
44349-9
Short code
Phe/Creat Ur
Synonyms
Phe/Creat Ur
Category
kidney
Sample
urine
Container
Sterile urine container
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
10 mL
Stability
Room temperature: 2h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

What is this test?

This test measures the amount of phenylalanine in urine relative to the amount of creatinine. Creatinine is used as an adjustment for urine concentration, so the ratio can help show how much phenylalanine is being excreted.

Why might I need this test?

The test may be used to monitor people with phenylketonuria, an inherited condition in which the body cannot process phenylalanine normally. It may also be part of an evaluation for abnormal phenylalanine metabolism.

How is the test performed?

A urine sample is tested to determine the concentrations of phenylalanine and creatinine. The laboratory then calculates the phenylanine-to-creatinine ratio from these measurements.

How do I prepare for the test?

Collect the urine sample in the container and at the time specified by your healthcare professional or laboratory. Your diet and medications may affect the result, so tell the care team about phenylalanine supplements, special formulas, medicines, and major changes in protein intake.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Urine phenylalanine/creatinine ratio

Frequently asked questions

Is this the same as a newborn screening test?
No. Newborn screening usually uses blood or urine testing, but this ratio is most often used to assess or monitor phenylalanine metabolism after screening or diagnosis.
Does a high result always mean phenylketonuria?
No. A high ratio can have several causes and must be interpreted with diet, medications, urine concentration, and other laboratory findings. Blood testing may be needed to confirm whether phenylalanine metabolism is abnormal.
Why is creatinine included in the result?
Creatinine helps account for how concentrated the urine is. This makes the phenylalanine-to-creatinine ratio more useful than an unadjusted urine phenylalanine measurement.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy