Free testosterone is the fraction of circulating testosterone that is not bound to sex-hormone–binding globulin (SHBG) or albumin, making it biologically active. Because it can freely enter cells and bind androgen receptors, free testosterone drives key physiological processes in both men and women.
Key Functions
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Muscle & Bone Health: Promotes muscle protein synthesis and maintains bone density.
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Mood & Cognition: Supports energy, motivation, and overall well-being.
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Libido & Sexual Function: Regulates sex drive, erectile function in men, and sexual arousal in women.
Normal Reference Ranges
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Men: 15.0–50.0 pg/mL
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Women: < 6.5 pg/mL
Clinical Indications
A free testosterone test may be ordered to evaluate:
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Hypogonadism: Low testosterone production in men.
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Erectile Dysfunction: Identifying hormonal causes.
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Polycystic Ovary Syndrome (PCOS): Androgen excess in women.
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Delayed or Precocious Puberty: In adolescents.
Signs & Symptoms
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Low Free T: Fatigue, low libido, muscle weakness, depression, reduced bone density.
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High Free T: Acne, oily skin, increased body/facial hair, voice deepening, aggression.
Diagnosis & Testing
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Specimen: Blood draw, typically in the morning when hormone levels peak.
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Assay: Equilibrium dialysis or analog immunoassays for accurate quantification.
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Interpretation: Correlated with total testosterone, SHBG levels, and clinical presentation.
Management
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Low Free T: Testosterone replacement therapy (TRT), weight management, resistance exercise.
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High Free T: Treat underlying conditions (e.g., PCOS), use of anti-androgens, lifestyle modifications.
Frequently Asked Questions
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Why measure free instead of total testosterone?
Free testosterone reflects the bioavailable hormone that directly influences tissues. -
How is the free testosterone test performed?
A morning blood sample is collected after an overnight fast (if possible). -
What causes low free testosterone?
Causes include aging, pituitary disorders, chronic illness, obesity, and certain medications. -
Can high free testosterone be harmful?
Yes—persistent elevations can lead to metabolic issues, cardiovascular risks, and virilization. -
How can I naturally boost free testosterone?
Regular strength training, adequate sleep, weight loss (if overweight), and ensuring sufficient vitamin D and zinc intake.
