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Serum or plasma mass concentration of free (unbound) testosterone

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

This test measures the amount of testosterone that is not attached to proteins in your blood, which can affect how your body uses this hormone.

Quick summary

["Free testosterone helps assess hormone balance, especially in conditions involving sex hormone regulation."]

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

Key facts at a glance

LOINC
30248-9
Short code
sTfR SerPl-mCnc
Synonyms
sTfR SerPl-mCnc
Category
coagulation
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 This Test Might Be Ordered

Your healthcare provider may recommend this test if you have symptoms related to hormone imbalances, such as irregular menstrual cycles, low libido, or signs of androgen excess or deficiency. It may also be used in fertility evaluations, endocrine disorders, or monitoring hormone therapy.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for 8–12 hours before the draw if your lab uses a specific protocol. Wear a loose shirt for easy access to your arm.

How the Test Works

Blood is drawn from a vein, typically in your arm. The sample is then processed to separate serum or plasma, where free testosterone is measured using a sensitive analytical method to detect its concentration accurately.

What the Results Mean

Results are compared to general reference ranges for free testosterone, though individual ranges may vary by lab. Abnormal levels may signal conditions like polycystic ovary syndrome, Cushing’s syndrome, or hypogonadism.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free testosterone level

Frequently asked questions

What does a low free testosterone level indicate?
Low free testosterone may suggest conditions like hypogonadism (low testosterone production), pituitary disorders, or liver/kidney dysfunction that affect hormone metabolism. It can also be seen in aging or chronic illness.
What does a high free testosterone level indicate?
High free testosterone may point to androgen excess, such as polycystic ovary syndrome (PCOS), tumors producing excess hormones, or certain medications. It can cause symptoms like acne, irregular periods, or male-pattern baldness in women.
Does fasting affect this test?
Fasting may not typically impact free testosterone levels, as they are not influenced by recent food intake. However, always follow your lab’s specific instructions to ensure accurate results.
  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