Skip to content

Serum Codeine Concentration (Free)

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

This test measures the amount of free (unbound) codeine in your serum. Codeine is a pain reliever that your body converts into morphine.

Quick summary

["Understanding your free codeine levels helps assess pain management and potential side effects."]

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

Key facts at a glance

LOINC
16644-7
Short code
Codeine Free SerPl Ql Cfm
Synonyms
Codeine Free SerPl Ql Cfm
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
confirm
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why This Test Is Done

Your healthcare provider may order this test if you’re taking codeine for pain relief and want to check how much of the drug is actively circulating in your blood. It can also help monitor for side effects like drowsiness or respiratory issues, especially if you’re taking higher doses or combining it with other medications.

What to Expect Before the Test

No special preparation is needed. You’ll have a small needle inserted into your arm or vein to draw blood. The process usually takes a few minutes. If you’re on blood thinners, let your provider know before the test.

What the Results Mean

Results are compared to a general reference range for free codeine in serum. High levels may indicate overuse, poor metabolism, or interactions with other medications. Low levels might suggest insufficient dosing or rapid metabolism.

Common Causes of Abnormal Results

Elevated levels could be due to recent codeine use, liver issues (since codeine is metabolized there), or other medications that slow its breakdown. Very low levels might mean your body processes codeine too quickly or you’re not taking enough as prescribed.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free Codeine Level

Frequently asked questions

How long does it take to get my test results?
Results are typically available within 1–3 business days, depending on your lab and insurance. Follow-up with your provider to discuss the findings and next steps.
Can I drink alcohol before this test?
Alcohol doesn’t directly affect codeine levels, but it can increase side effects like drowsiness. Avoid heavy drinking before testing if you’re concerned about medication interactions.
Will I need to fast for this test?
No fasting is required. Blood tests like this are usually done on an empty stomach, but if you’re unsure, ask your provider. Your provider will guide you based on your specific 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