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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 free (not protein-bound) testosterone in your blood. Free testosterone is the active form that your body uses.

Quick summary

["Understanding your free testosterone levels can help assess hormone balance and potential hormone-related health concerns."]

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

Key facts at a glance

LOINC
39887-5
Short code
NM Hrt FP+EF Rest+W RNC IV
Synonyms
NM Hrt FP+EF Rest+W RNC IV
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
nm
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 Matters

Free testosterone is crucial for hormone regulation, especially in both men and women. It helps maintain energy levels, muscle mass, and reproductive health. Abnormal levels may indicate conditions like hormonal imbalances, infertility, or other health issues.

What to Expect Before the Test

No special preparation is usually needed, but your doctor may advise avoiding certain medications or activities for a few days before testing. You’ll provide a blood sample, typically drawn from your arm.

What the Results Mean

Results are compared to general reference ranges for your age, sex, and health status. Low levels might suggest conditions like hypogonadism, while high levels could indicate hormonal disorders or other medical issues.

Common Conditions This Test Helps Diagnose

This test is often used to diagnose or monitor conditions like low testosterone (hypogonadism), polycystic ovary syndrome (PCOS), or other hormonal imbalances. It can also help evaluate fertility and symptoms like low libido or fatigue.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free testosterone level

Frequently asked questions

What causes free testosterone levels to be low?
Low free testosterone can result from conditions like pituitary disorders, primary hypogonadism, obesity, aging, or certain medications. Lifestyle factors, such as poor diet or lack of exercise, may also play a role.
What causes free testosterone levels to be high?
High free testosterone levels may be due to tumors affecting the adrenal or gonadal glands, genetic conditions, or certain medications. It can also occur in conditions like Cushing’s syndrome or androgen-producing tumors.
How often should I get this test?
Your doctor will determine the frequency based on your symptoms, medical history, and treatment plan. Typically, tests may be repeated every few months or annually if monitoring ongoing conditions like hormone therapy or fertility treatments.
  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