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Serum or plasma concentration of free (unbound) testosterone

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

This test measures the amount of testosterone in your blood that is not attached to proteins, giving a direct measure of biologically active testosterone.

Quick summary

["Understanding your free testosterone levels helps assess hormone balance, especially in conditions affecting sex hormones."]

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

Key facts at a glance

LOINC
33171-0
Short code
GS Diam from GA.Rempen91
Synonyms
GS Diam from GA.Rempen91
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-estimated-from-rempen
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 to evaluate hormone function, diagnose conditions like hypogonadism (low testosterone), or monitor treatment for hormone-related disorders. It’s also used in fertility evaluations or before certain surgeries.

How the Test Works

Blood is drawn, and the test measures unbound testosterone levels using a sensitive immunoassay method. This avoids interference from protein-bound testosterone, which can skew results if not separated.

Sample Preparation

The test uses either serum (blood after clotting) or plasma (blood after centrifugation). Your provider will specify which type is needed based on clinical context.

What to Expect Before the Test

No special preparation is usually required, but avoid smoking or consuming alcohol 24 hours before testing, as these can affect hormone levels.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Elevated free testosterone may indicate conditions like Cushing’s syndrome or androgen-secreting tumors, while low levels can signal hypogonadism, pituitary disorders, or obesity. It’s particularly useful for diagnosing gender dysphoria or evaluating androgen-related symptoms in women.

Short name

Free testosterone level

Frequently asked questions

What does a high free testosterone level mean?
A high result may suggest overproduction of testosterone by the adrenal glands or ovaries/testes, or conditions like polycystic ovary syndrome (PCOS) in women. Always discuss results with your provider, as they’ll consider your full medical history and symptoms.
What does a low free testosterone level mean?
Low levels can result from conditions like Klinefelter syndrome, pituitary disorders, or aging. It may also occur in women with premature ovarian insufficiency or after certain medications. Your provider will review your symptoms and other test results to guide next steps.
How often should I get this test?
Frequency depends on your health needs. Routine checks for men over 40 or women with hormonal symptoms may occur every 1–3 years, but your provider will tailor recommendations based on your specific situation.
  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