Free Testosterone
- Sample Type
- Serum
- Fasting
- Required
- Unit
- pg/mL
Function
Free Testosterone measures the amount of testosterone in the blood that is not bound to Sex Hormone-Binding Globulin (SHBG) or albumin. While total testosterone represents the whole reservoir, free testosterone is the 'bioavailable' portion—the hormone that is actually free to enter cells and trigger biological effects. It plays a critical role in libido, bone density, muscle mass, and mood regulation.
Why it is Ordered
This test is ordered when Total Testosterone results are borderline or when a patient has conditions that alter SHBG levels (like obesity, liver disease, or thyroid issues), which can make Total Testosterone results misleading. In men, it is used to investigate erectile dysfunction or low libido. In women, it is primarily used to investigate symptoms of 'virilization' such as excess facial hair (hirsutism) or irregular periods.
Associated Conditions
- Hypogonadism (Men): Low levels lead to fatigue, muscle loss, and sexual dysfunction.
- Polycystic Ovary Syndrome (PCOS): High levels in women are a hallmark of this endocrine disorder.
- Androgen Insensitivity: High levels of testosterone with low clinical effect.
- Hirsutism: Excessive hair growth in women due to elevated bioavailable androgens.
Check Your Result
Check Your Result
Enter your lab result to see where you stand compared to the standard reference range.
Why Context Matters
Testosterone levels follow a circadian rhythm, peaking in the early morning (7 AM - 10 AM). Tests taken in the afternoon often yield falsely low results. Furthermore, acute stress, lack of sleep, and intensive exercise 24 hours prior can significantly alter levels. Biotin supplements also interfere with most hormone assays. Because 'Free' testosterone is often calculated rather than measured directly, different laboratory formulas (e.g., Vermeulen) can yield different results, necessitating a second check.
Lab ranges are statistical averages, not biological laws. "Normal" for a 20-year-old male isn't normal for a 60-year-old female.
Clinical References
Source-of-truth databases and clinical guidelines for Free Testosterone:
Official Sources
Research & Guidelines
- PubMed: Free Testosterone Clinical GuidelinesNCBI / PubMed
Related Indicators
Medically Reviewed by Dr. Binoy Babu, MBBS
Board Certified Doctor • 10+ Years Clinical Experience
Dr. Babu is a practicing physician dedicated to empowering patients with clear, actionable medical information. He founded 2opi to bridge the gap between complex lab reports and patient understanding, ensuring everyone has access to a reliable second opinion.
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