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Mephenytoin in Urine (24-Hour Collection)

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

This test measures the amount of mephenytoin, a medication used to diagnose certain genetic conditions affecting how your body processes drugs, in your urine over a 24-hour period.

Quick summary

["Helps assess how your body breaks down medications linked to inherited metabolic disorders."]

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

Key facts at a glance

LOINC
111238-2
Short code
Me-phenidate Msmt Ur
Synonyms
Me-phenidate Msmt Ur
Category
chemistry
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

Why This Test Is Done

Your doctor may order this test if you have a family history of conditions like phenylketonuria (PKU) or other metabolic disorders that affect drug metabolism. It helps evaluate whether your body processes mephenytoin normally, which can indicate genetic predispositions to drug-related issues.

What to Expect Before the Test

You’ll need to collect all urine produced in a 24-hour period in a special container. Drink plenty of fluids to ensure full collection, and follow your healthcare provider’s instructions precisely to avoid contamination or incomplete results.

How the Test Works

The collected urine sample is analyzed to measure the concentration of mephenytoin, a drug used in metabolic screening. The test detects how efficiently your body metabolizes this compound, which can reflect broader metabolic function.

What the Results Mean

Results are compared to expected ranges for healthy individuals. Abnormal levels may suggest inherited metabolic disorders or impaired drug processing, prompting further genetic testing or medical evaluation.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: Understanding Results

Short name

24-Hour Mephenytoin Urine

Frequently asked questions

What might cause abnormal results?
Abnormal results could indicate genetic conditions affecting drug metabolism, such as certain forms of phenylketonuria or other inherited enzyme deficiencies. They may also suggest how your body processes other medications differently.
How long will it take to get results?
Results are typically available within 1 to 2 weeks after the sample is processed, depending on lab workload and testing protocols.
Can I take any medications before this test?
No, avoid mephenytoin-containing medications (e.g., certain metabolic tests or diagnostic drugs) and consult your doctor about other medications to stop temporarily, as they may interfere with the test.
  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