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Phenylalanine/Creatinine Ratio, Urine

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

A urine test that compares phenylalanine with creatinine to help assess phenylalanine levels and monitor treatment for phenylketonuria.

Quick summary

["This ratio helps clinicians monitor whether phenylalanine levels are appropriately controlled."]

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

Key facts at a glance

LOINC
30055-8
Short code
Phe/Creat Ur-Rto
Synonyms
Phe/Creat Ur-Rto
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 relative to creatinine in a urine sample. Creatinine is used to help account for how concentrated or dilute the urine is.

Why might I need this test?

It is most often used to monitor people with phenylketonuria, or PKU, and assess how well dietary or medical treatment is controlling phenylalanine levels.

How is the test performed?

A urine sample is analyzed for phenylalanine and creatinine. The laboratory then calculates the phenylalanine-to-creatinine ratio.

How do I prepare for the test?

Follow your clinician's instructions about urine collection and timing. Do not make major changes to your prescribed protein or phenylalanine intake shortly before testing, because dietary changes can affect the result.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Urine phenylalanine-to-creatinine ratio

Frequently asked questions

What does the urine phenylalanine-to-creatinine ratio measure?
It compares the amount of phenylalanine in urine with the amount of creatinine. This helps reduce the effect of variations in urine concentration.
Is this test used to screen for PKU?
Newborn screening is usually performed with blood tests. Urinary phenylalanine-to-creatinine ratio is more commonly used to monitor treatment and dietary control in people already diagnosed with PKU.
Does an abnormal result mean I am not taking my treatment correctly?
Not necessarily. Illness, changes in diet or medication, and other factors can also affect the result, so your clinician will interpret it together with other information.
  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