Serum/plasma free fraction of a substance measured by immunoassay (e.g., free fraction of a drug or hormone)
This test evaluates the amount of a specific substance in your blood that is not bound to proteins, which can affect how your body processes it.
Understanding free fractions helps doctors assess drug levels or hormone activity more accurately.
Key facts at a glance
- LOINC
- 72576-2
- Short code
- PSA Free MFr.DF SerPl
- Synonyms
- PSA Free MFr.DF SerPl
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 0
- Ref high
- 4
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 84153
- SNOMED
- 39392002
- 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
What This Test Measures
The test looks at the portion of a substance (like a medication or hormone) that is freely available in your bloodstream, separate from proteins that might bind to it. This free fraction can influence how your body uses or removes the substance.
Why It Matters in Medicine
Free fractions are important for certain medications (e.g., drugs metabolized by the liver) or hormones where protein binding can alter activity. For example, free drug levels may be critical for dosing in kidney or liver disease.
Common Uses
This test may be used when monitoring medications that rely on free concentration for safety or effectiveness, such as certain cancer treatments or psychiatric drugs.
Sample Collection and Preparation
Blood is drawn into a tube that separates serum or plasma from cells. The test then measures the unbound portion of the substance using a sensitive immunoassay method.
Reference range
Normal: <4.0 ng/mLN/A
No special preparation required. For PSA, avoid sexual activity for 24-48 hours before the test.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance
Frequently asked questions
How does the free fraction of a substance differ from the total amount measured in a standard test?
What conditions might require this specific test over a standard total measurement?
Could this test be used for routine screening, or is it typically ordered based on specific symptoms or medical needs?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
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.
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