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Serum/plasma free testosterone concentration

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 the hormone responsible for male and female sex characteristics.

Quick summary

["Free testosterone helps regulate energy, mood, and reproductive health."]

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

Key facts at a glance

LOINC
46415-6
Short code
LH 45M p GnRH SerPl-aCnc
Synonyms
LH 45M p GnRH SerPl-aCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
1.5
Ref high
9
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
83002
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 Does Free Testosterone Measure?

Free testosterone is the portion of total testosterone that isn’t bound to proteins in your blood. It’s the form that directly affects your body’s tissues, influencing muscle mass, libido, and hormone balance. Unlike total testosterone, free testosterone isn’t diluted by protein carriers, so it reflects your true biological activity.

Why Is Free Testosterone Important?

Free testosterone plays a key role in maintaining energy levels, muscle strength, and sexual function. It also supports cognitive function and mood stability. Low levels may be linked to symptoms like fatigue, low libido, or hormonal imbalances.

How Is This Test Performed?

A blood sample is drawn from a vein in your arm. The test measures the unbound (free) testosterone in your serum or plasma, typically analyzed using immunoassay methods like chemiluminescent immunoassay (CLIA) or fluorescence immunoassay (FIA).

When Might You Need This Test?

Your doctor may order a free testosterone test if you have symptoms of hormonal imbalances, such as low energy, reduced sex drive, or irregular menstrual cycles (in women). It’s also used in fertility evaluations, androgen deficiency assessments, or monitoring conditions like polycystic ovary syndrome (PCOS).

Reference range

Follicular: 1.5-9.0 mIU/mLN/A

Specimen: serum

For females: inform if menstrual cycle status. For certain tests, timing within menstrual cycle may matter.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free testosterone

Frequently asked questions

Why do I need this test if my total testosterone is normal?
Total testosterone includes both free and bound forms, so it may not always reflect your active hormone levels. Free testosterone gives a clearer picture of your biological activity, especially if you have conditions that affect protein binding (e.g., liver disease or obesity).
What are the typical reference ranges for free testosterone?
Reference ranges vary by lab and age/gender. For men, they typically fall between 60–300 pg/mL, while women’s ranges are lower (around 10–70 pg/mL). Your doctor will compare your result to your specific baseline and clinical needs.
Can lifestyle changes affect free testosterone levels?
Yes! Factors like diet (e.g., high-fat or processed foods), exercise, stress, and sleep quality can influence testosterone levels. Maintaining a balanced diet, regular physical activity, and managing stress may support healthy hormone levels.
  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