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Free testosterone (serum/plasma, calculated 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 this hormone.

Quick summary

["Free testosterone helps regulate sex hormones and supports health in both men and women."]

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

Key facts at a glance

LOINC
103227-5
Short code
Testost Free SerPl Calc-mCnc
Synonyms
Testost Free SerPl Calc-mCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
calculated
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 this test to evaluate hormone balance, diagnose conditions like hypogonadism or polycystic ovary syndrome (PCOS), or assess symptoms such as low libido, irregular periods, or fatigue. It can also help monitor treatment for hormone-related disorders.

What Does It Measure?

Free testosterone is the portion of testosterone that is not bound to proteins in your blood. This unbound form is biologically active and can be measured directly or calculated from total testosterone levels and protein binding ratios.

Sample Collection and Preparation

A blood sample is drawn from a vein, usually in the arm. The sample is processed to separate serum or plasma, then analyzed to determine the concentration of free testosterone.

What Might Affect Results?

Several factors can influence free testosterone levels, including medications (e.g., steroids, birth control), certain health conditions (e.g., obesity, thyroid disorders), stress, and lifestyle habits like smoking or alcohol use. Recent exercise or fasting can also temporarily affect results.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free Testosterone

Frequently asked questions

How is this test different from total testosterone?
Free testosterone is the active, unbound form of testosterone, while total testosterone includes both free and protein-bound testosterone. Free testosterone is more directly linked to biological effects, so it is often used to assess hormone activity.
What are the typical reference ranges for free testosterone?
Reference ranges vary by lab and individual factors like age, sex, and health status. Your results will be compared to ranges specific to your demographic and clinical context.
Can diet or supplements affect my free testosterone levels?
Certain foods, vitamins, and supplements (e.g., zinc, vitamin D, or herbal products like saw palmetto) may influence hormone levels. It’s best to discuss any supplements or dietary changes with your healthcare provider before testing.
  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