Skip to content

Serum or Plasma Free Testosterone (by Immunoassay)

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

This test measures the amount of free (unbound) testosterone in your blood, which is the active form of this hormone.

Quick summary

["Free testosterone helps regulate sex hormones and supports overall health, including muscle and bone strength."]

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

Key facts at a glance

LOINC
100876-2
Short code
Fet Hrt Doc US
Synonyms
Fet Hrt Doc US
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
us
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 Might Be Ordered

Your healthcare provider may recommend this test if you have symptoms related to hormone imbalances, such as low libido, fatigue, or irregular menstrual periods. It could also be used to monitor conditions like polycystic ovary syndrome (PCOS), infertility, or hormonal therapy responses.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the draw if your lab requires it. Wear comfortable clothing for blood draws, and let your provider know about any medications or supplements you take.

What the Test Involves

A small needle will be used to draw blood from a vein in your arm. The process usually takes a few minutes. You may feel slight discomfort, but it should subside quickly. The blood sample is then sent to a lab for analysis.

What the Results Mean

Results help determine if your free testosterone levels are within a typical range for your age and sex. Abnormal results may prompt further evaluation to check for conditions affecting hormone production or metabolism.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free testosterone

Frequently asked questions

How does free testosterone differ from total testosterone?
Free testosterone is the portion of testosterone that is unbound to proteins in the blood and thus biologically active. Total testosterone includes both free and protein-bound forms, so free testosterone gives a clearer picture of your hormone’s direct impact on the body.
What conditions might affect free testosterone levels?
Conditions like obesity, thyroid disorders, chronic illnesses, or certain medications can influence testosterone levels. If you suspect an issue, discuss symptoms with your provider—they may recommend additional tests or adjustments to treatment.
Can lifestyle changes impact free testosterone levels?
Yes, diet, exercise, stress management, and avoiding smoking or excessive alcohol can positively affect hormone levels. Maintaining a healthy weight, getting regular physical activity, and reducing stress may support balanced hormone function.
  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