Total vs. free testosterone: what's the difference, and which should you test?

Quick answer: should I measure total or free testosterone?
Start with a Total Testosterone Blood Test. It's the standard first-line test and is usually enough to show whether your levels are low. Get a Free and Total Testosterone Blood Test if your total is borderline, you still have symptoms despite a normal result, or something is likely to be pushing your SHBG up or down (age, obesity or insulin resistance, thyroid or liver disease, certain medications).

Testosterone is a vital hormone for both men and women. But if you’ve ever taken a testosterone blood test before, you’ve probably noticed there are two different types: total and free. Both can be helpful to establish whether your testosterone levels are low, but what’s the difference? 

In this article, we cover:  

• Free vs total testosterone
• Free testosterone in women (FAI)
• What is bioavailable testosterone? 
• What is a normal free testosterone level? 
• Can you have normal total testosterone but low free testosterone? 
• Can you have low total testosterone but normal free testosterone?
• How can I increase free testosterone levels?  
• Should I test free or total testosterone? 

Free vs total testosterone: the difference
 

Once testosterone is made, it enters the bloodstream. But because it doesn’t dissolve, most testosterone (about 95%) catches a ride on other proteins, like sex hormone-binding globulin (SHBG) and albumin.

When testosterone is bound to a protein, it’s inactive. It can’t act on tissues until it’s released. There are two benefits to this: 

• It regulates testosterone activity 
• It prevents the liver and kidneys from deactivating and removing testosterone too soon 

Once it reaches its target cell, testosterone binds to specific receptors and triggers changes within the cell.  

What is total testosterone?

Total testosterone is a total measure of testosterone in the bloodstream, both free and bound. Levels are measured by an analyser directly.  

What is free testosterone?

Free testosterone is the concentration of testosterone in the blood that is not attached to proteins. Only about 2–5% of testosterone is free. You can measure free testosterone directly, but it's challenging and not widely available, so it's often calculated instead using total testosterone, SHBG, and albumin. 
 

Free testosterone in women 
 

In women, testosterone levels are around ten times lower than men, and about 80% is bound to SHBG. This makes accurate measurement of free testosterone important. 

When investigating raised androgens for conditions like polycycstic ovary syndrome (PCOS), often we calculate free androgen index (FAI) instead. FAI ignores albumin completely and instead looks at the ratio of testosterone relative to SHBG. 

However, calculated free testosterone may be more reliable, particularly when SHBG is low [1].

 

What is bioavailable testosterone?

Bioavailable testosterone is just any testosterone that's available and able to act to tissues. Free testosterone falls into this category, since it can bind to cell receptors as it pleases. 

But testosterone bound to albumin is also classed as bioavailable. That’s because the testosterone-albumin bond is easily reversible, meaning testosterone frequently switches between active and inactive forms. This effect is greater in men because more of their testosterone binds to albumin.

Bioavailable testosterone is a measure of testosterone that is readily available to act on tissues. It's calculated by adding free testosterone to albumin-bound testosterone.

What is a normal free testosterone level?

Normal free testosterone is roughly 0.2–0.62 nmol/L in men and 0.001–0.02 nmol/L in women. Levels vary according to the laboratory, so the table below is given as a guide.  

	Men	Women
Total testosterone (nmol/L)	8.7–29	Age 20–49: 0.29–1.67 Age 50 or over: 0.1–1.42
Free testosterone (nmol/L)	0.2–0.62	0.001–0.02
Free androgen index (%)	Rarely measured	0.18–7.07
Albumin (g/L)	35–50	35–50
SHBG (nmol/L)	18.3–54	27–146

Testosterone levels vary according to life stage. Find out more about how testosterone levels decline with age. 
 

Can you have normal total testosterone and low free testosterone?

Yes, it’s possible to have normal total testosterone levels but low free testosterone, which may lead to symptoms of testosterone deficiency.  

As we’ve seen, it’s the bioavailable portion of testosterone that exerts its effects on the body. So, if SHBG levels are particularly high relative to total testosterone, it won’t leave much free testosterone to act on tissues. This can be seen in older age, where SHBG levels often increase considerably [2].  

Other causes of raised SHBG levels include [3]:  

• Medications – such as oestrogens and anti-epilepsy drugs
• Conditions – such as liver disease, an overactive thyroid (hyperthyroidism), and HIV 
   

Can you have low total testosterone but normal free testosterone levels?
 

The opposite is also true: total testosterone levels may appear low when free testosterone levels are within normal range. This is most often seen in men in the development of insulin resistance (obesity or diabetes), which often causes SHBG levels to decline. Therefore, less testosterone is bound to proteins [2].

You can check your blood sugar control from home with our Diabetes (HbA1c) Blood Test.
 

How can I increase free testosterone levels?
 

Free testosterone levels are dependent on both total testosterone levels and your levels of SHBG (the protein that binds to it).  

Therefore, increasing your total testosterone level through healthy lifestyle choices is also likely to increase your free testosterone levels. Factors like stress, low levels of activity, and being overweight can all impact your testosterone production. There are many ways you can boost testosterone levels naturally, from losing weight to maintaining a healthy, balanced diet.  

If your SHBG levels are abnormally high, it’s worth exploring whether medications or an underlying health condition may be playing a part in this.
 

Should I test total or free testosterone?

The answer to this question will depend on why you’re testing and your gender.

Men

If you’re curious, or just want to make sure you’re not deficient, total testosterone will likely give you your answer. This is usually the first step in investigating symptoms of hypogonadism (low testosterone) and makes a great screening test.  

If you have low or borderline total testosterone levels or you have ongoing symptoms, your doctor recommend measuring calculated free testosterone and SHBG alongside LH (to distinguish between different types of hypogonadism) and, where indicated, FSH (if fertility is an issue) [4–6]. You can check your free testosterone levels at home with our finger-prick Free and Total Testosterone Blood Test, or if you'd also like to test for the other hormones mentioned, try our Male Hormone Blood Test. 

There is some evidence that free testosterone may be more useful when investigating testosterone deficiency [1], because total testosterone may be normal even when free testosterone is low.  

Women 

When investigating androgen excess (raised male hormones) in women, including PCOS, clinicians may measure total testosterone, SHBG and calculated free testosterone [1]. FAI can also be used, but may be less reliable when SHBG is low.

Other hormones like luteinising hormone (LH), follicle-stimulating hormone (FSH) and prolactin are sometimes also measured to rule out other causes of irregular periods.  

Some women suspect their testosterone levels are low because they have low libido, but the two don't always correlate. It’s likely that the metabolism of testosterone, rather than absolute levels, is a more important determinant of libido, which can’t be measured [7].  

If testosterone treatment is considered for low sexual desire, the BMS recommends checking total testosterone before treatment and during monitoring, rather than FAI or free testosterone [7].

Trans and non-binary people on hormone therapy 

If you're on gender-affirming hormone therapy, blood tests are used to monitor testosterone and, where relevant, oestradiol alongside clinical changes.

Guidelines recommend monitoring hormone levels approximately every three months during the first year, then once or twice yearly after stabilisation [8,9]. If hormone levels and physical changes don't align, assessing SHBG and free testosterone can sometimes provide useful context [10].

When taking hormone medication, it’s important to make sure you’re taking your blood test at the right time. And if you use hormone gels and are taking a finger-prick test, you should make sure your finger is completely clear of any hormone gel to avoid an abnormally high result, or ideally take a venous test. 
 

The bottom line 
 

Testosterone is more complicated than it seems at first glance. To summarise, total testosterone is a helpful biomarker to measure if you’re experiencing symptoms of low or raised levels. This can be combined with free testosterone or a free androgen index for a better idea of bioavailable testosterone levels.
 

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References

 

1. Elhassan YS, Hawley JM, Cussen L, Abbara A, Clarke SA, Kempegowda P, et al. Society for Endocrinology Clinical Practice Guideline for the Evaluation of Androgen Excess in Women. Clin Endocrinol (Oxf). 2025;103(4):540–566.
2. Antonio L, Wu FCW, O'Neill TW, Pye SR, Ahern TB, Laurent MR, et al. Low Free Testosterone Is Associated with Hypogonadal Signs and Symptoms in Men with Normal Total Testosterone. J Clin Endocrinol Metab. 2016;101(7):2647–2657.
3. Bhasin S, Brito JP, Cunningham GR, Hayes FJ, Hodis HN, Matsumoto AM, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2018;103(5):1715–1744.
4. Hackett G, Kirby M, Rees RW, Jones TH, Muneer A, Livingston M, et al. The British Society for Sexual Medicine Guidelines on Male Adult Testosterone Deficiency, with Statements for Practice. World J Mens Health. 2023;41(3):508–537.
5. Jayasena CN, de Silva NL, O'Reilly MW, MacKenzie F, Marrington R, Jones H, et al. Standardising the biochemical confirmation of adult male hypogonadism: a joint position statement by the Society for Endocrinology and Association of Clinical Biochemistry and Laboratory Medicine. Clin Endocrinol (Oxf). 2024;101(5):531–534.
6. Corona G, Morgado LA, Boeri L, Capogrosso P, Cocci A, Dinkelman-Smit M, et al. EAU Guidelines on Sexual and Reproductive Health: A Summary of the 2026 Recommendations for Measurement and Biochemical Confirmation of Hypogonadism. Eur Urol Focus. 2026 May 23. Online ahead of print. doi:10.1016/j.euf.2026.04.015.
7. Panay N. Testosterone replacement in menopause. Post Reprod Health. 2026;32(2):130–134.
8. Coleman E, Radix AE, Bouman WP, Brown GR, de Vries ALC, Deutsch MB, et al. Standards of Care for the Health of Transgender and Gender Diverse People, Version 8. Int J Transgend Health. 2022;23(Suppl 1):S1–S259.
9. Hembree WC, Cohen-Kettenis PT, Gooren L, Hannema SE, Meyer WJ, Murad MH, et al. Endocrine Treatment of Gender-Dysphoric/Gender-Incongruent Persons: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2017;102(11):3869–3903.
10. Maheshwari A, Nippoldt T, Davidge-Pitts C. An Approach to Nonsuppressed Testosterone in Transgender Women Receiving Gender-Affirming Feminizing Hormonal Therapy. J Endocr Soc. 2021;5(9):bvab068.