Quick answer: Free testosterone is the small fraction of testosterone that is not bound to proteins and can act on tissues. It is especially useful when SHBG is high or low, because total testosterone can look normal while free testosterone is low, or vice versa. It helps evaluate low-T symptoms in men and androgen excess in women.
Key takeaways
Free testosterone is the small unbound fraction that can actually act on tissues.
It is especially useful when SHBG is high or low, because total testosterone can look normal while free testosterone is not.
It helps evaluate low-testosterone symptoms in men and androgen excess in women.
What is Free Testosterone?
Most testosterone is bound to SHBG or albumin. Free testosterone is the unbound portion available to cells.
Why Free Testosterone matters
Free testosterone reflects active testosterone and clarifies results when SHBG is abnormal. It is also used to evaluate PCOS and androgen excess in women.
Understanding your result
Reference ranges vary by lab, age and sex. Your provider interprets your result against the lab’s range and your overall picture, rather than chasing a single number. Functional labs are optional. They can be helpful in more complex cases.
What low Free Testosterone can mean
Low free testosterone can reflect high SHBG (aging, hyperthyroidism, low-calorie diets), low total testosterone, or poor sleep and chronic stress.
What high Free Testosterone can mean
High free testosterone can reflect low SHBG from insulin resistance, PCOS, or testosterone or steroid use.
What affects Free Testosterone
Free testosterone is affected by SHBG levels, insulin, thyroid function, and the test method (calculated or measured).
Ways to support healthy levels
Improve insulin sensitivity (see SHBG), strength train, sleep well, and eat enough protein and calories. Read the result alongside total testosterone.
What does the research show about free testosterone?
The European Male Ageing Study surveyed a random sample of 3,369 men aged 40 to 79 in eight countries and measured morning testosterone with mass spectrometry. Only three sexual symptoms, poor morning erections, low sexual desire and erectile dysfunction, clustered with low testosterone, and the researchers proposed defining late-onset low testosterone as those three symptoms plus total testosterone below 11 nmol/L (about 320 ng/dL) and free testosterone below 220 pmol/L (about 64 pg/mL). The study was cross-sectional and mostly in European men, so it cannot show cause and effect. (Wu et al., 2010)
In the UK Biobank, researchers followed 149,436 men aged 40 to 69 for about 11 years, during which 10,053 died. Men in the lowest fifth of testosterone had a 14% higher death rate than those in the highest fifth (hazard ratio 1.14), and calculated free testosterone showed similar results, while men with the lowest SHBG had a 32% lower death rate than those with the highest (hazard ratio 0.68). Testosterone was measured once by immunoassay, and observational data cannot show that changing these levels would change risk. (Yeap et al., 2021)
Free testosterone is usually calculated from total testosterone, SHBG and albumin, so the accuracy of the result depends on all three measurements.
Free Testosterone and healthy aging
Active testosterone supports muscle, bone and metabolic health, and its tendency to decline with age is linked with muscle loss.
When to see a naturopathic doctor
It may be time to see a naturopathic doctor if you have low-T symptoms with normal total testosterone, or signs of PCOS. The same is true if your SHBG is abnormal, or if you want hormone results explained.
Free Testosterone at a glance
| Topic | What the article explains |
|---|---|
| Why it matters | Reflects active testosterone; clarifies results when SHBG is abnormal; and evaluates PCOS and androgen excess in women |
| What can affect it | SHBG levels; insulin; thyroid; and test method (calculated or measured) |
| Supportive habits discussed | Improve insulin sensitivity; strength train and sleep well; eat enough protein and calories; and read alongside total testosterone |
Questions to bring to your clinician
These questions can help you get the most out of your next visit.
Should we measure free testosterone and SHBG rather than relying on total testosterone alone?
How should I read my free testosterone alongside the rest of my labs and my symptoms?
How often would it make sense to recheck my free testosterone in my situation?
Which daily habits or medications could be influencing my free testosterone before we retest?
Frequently asked questions
What is free testosterone?
The unbound portion of testosterone that can act on tissues.
Why is free testosterone low when total is normal?
High SHBG can bind more testosterone, lowering the free portion.
Is calculated free testosterone accurate?
Calculated values using total testosterone, SHBG and albumin are widely used.
Does free testosterone matter for women?
Sources
- Finkelstein JS, et al. Gonadal steroids and body composition, strength, and sexual function in men. N Engl J Med 2013. PMID: 24024838. https://pubmed.ncbi.nlm.nih.gov/24024838/
- Teede HJ, et al. Recommendations From the 2023 International Evidence-based Guideline for the Assessment and Management of Polycystic Ovary Syndrome. J Clin Endocrinol Metab 2023. PMID: 37580314. https://pubmed.ncbi.nlm.nih.gov/37580314/
- Vermeulen A, et al. A critical evaluation of simple methods for the estimation of free testosterone in serum. J Clin Endocrinol Metab 1999. PMID: 10523012. https://pubmed.ncbi.nlm.nih.gov/10523012/
- Wu FC, et al. Identification of late-onset hypogonadism in middle-aged and elderly men. N Engl J Med 2010. PMID: 20554979. https://pubmed.ncbi.nlm.nih.gov/20554979/
- Yeap BB, et al. Serum Testosterone is Inversely and Sex Hormone-binding Globulin is Directly Associated with All-cause Mortality in Men. J Clin Endocrinol Metab 2021. PMID: 33059368. https://pubmed.ncbi.nlm.nih.gov/33059368/
- MedlinePlus: Testosterone Levels Test
- MedlinePlus: SHBG Blood Test
This article is for educational purposes only and is not medical advice. It does not replace an individual evaluation. Talk with your healthcare provider before starting supplements or changing medications, especially if you are pregnant, nursing, or managing a health condition.
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