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Serum Free Morphine Concentration

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

This test measures the amount of free (unbound) morphine in your serum, which can help assess how much of the drug is actively circulating in your bloodstream.

Quick summary

["Understanding your free morphine levels helps doctors monitor pain relief and potential side effects."]

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

Key facts at a glance

LOINC
97281-0
Short code
Morphine Free TissCo Ql Cfm
Synonyms
Morphine Free TissCo 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 morphine or another opioid medication. Free morphine levels help determine how your body is processing the drug, especially if you have kidney issues or are taking other medications that might affect how morphine works in your body.

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 a blood sample. The process is quick and usually causes only mild discomfort.

What the Results Mean

Free morphine levels can vary based on factors like your metabolism, kidney function, and other medications you’re taking. High levels may indicate poor drug clearance, while very low levels might suggest inadequate pain relief.

Common Reasons for Testing

This test is often used in patients on long-term opioid therapy to adjust doses, manage side effects, or monitor for drug interactions. It’s also useful in cases of suspected opioid toxicity or withdrawal.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Free Morphine Level

Frequently asked questions

What does a high free morphine level mean?
A high free morphine level may suggest that your kidneys are not effectively removing the drug, which could lead to increased side effects like drowsiness, confusion, or respiratory depression. It may also indicate that your dose needs adjustment.
How does free morphine differ from total morphine?
Free morphine is the portion of the drug that is unbound and can directly affect your body. Total morphine includes both free and bound (protein-bound) forms. Free morphine is more relevant for assessing active drug levels and potential toxicity.
Can diet or other medications affect this test?
Yes, certain medications (like some antibiotics or antifungals) can alter how morphine is processed in your body, potentially affecting free morphine levels. Also, kidney function plays a key role—if your kidneys aren’t working well, morphine may stay in your system longer.
  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