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Serum/plasma mass concentration of free (unbound) testosterone

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

This test measures the amount of free testosterone in your blood, which is the form of testosterone that actively influences hormones and health. Free testosterone is not bound to proteins and is available to your body’s cells.

Quick summary

["Free testosterone helps regulate hormones, muscle mass, and energy levels."]

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

Key facts at a glance

LOINC
27829-1
Short code
GH sp8 p chal SerPl-mCnc
Synonyms
GH sp8 p chal SerPl-mCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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 Is This Test Done?

Your healthcare provider may order a free testosterone test to evaluate hormone balance, especially if you have symptoms like low energy, low libido, or changes in mood. It’s also used in fertility assessments, hormone replacement therapy planning, or to check for conditions like hypogonadism or Cushing’s syndrome.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the blood draw if your test includes other hormone measurements. Wear comfortable clothing and plan to rest afterward, as you might feel lightheaded.

What Happens During the Test?

A healthcare professional will draw blood from a vein in your arm. The sample is then sent to a lab for analysis. The process usually takes a few minutes, and you can resume normal activities immediately.

What Are the Results?

Results are compared to general reference ranges for free testosterone, though individual ranges may vary. Low levels may indicate hormonal imbalances, while very high levels could signal conditions like tumors or Cushing’s syndrome.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free testosterone level

Frequently asked questions

What causes low free testosterone?
Low free testosterone can result from aging, obesity, chronic illnesses (like diabetes or kidney disease), medications (e.g., steroids), or genetic conditions. Lifestyle factors like poor sleep or excessive alcohol use may also play a role.
What are the symptoms of abnormal free testosterone?
Symptoms of low free testosterone may include fatigue, reduced sex drive, muscle weakness, or mood changes. High levels might cause acne, irregular periods, or deepened voice in women, or hair loss in men.
How often should this test be repeated?
Your provider will determine follow-up timing based on your symptoms and test results. Some may recommend retesting every 6–12 months, especially if you’re undergoing hormone treatment or have ongoing health concerns.
  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