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If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.
In case you’re wondering, “free testosterone” does not mean testosterone replacement therapy at no cost. (Be wary of anyone offering anything like that, especially online).
In actuality, free testosterone is a type of testosterone we all have running through our veins. If you get your testosterone levels tested, your healthcare provider may want to test your total testosterone levels and your free testosterone levels. They’re both important.
In this article, we’ll give you the run-down on free testosterone and why it matters.
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What is free testosterone?
Most people are familiar with testosterone, but you might not know that you have both “bound testosterone” and “free testosterone.”
Most testosterone in your body is attached to one of two proteins: albumin and sex hormone-binding globulin (SHBG). However, a small amount of testosterone (2-5%) is unattached, otherwise known as “free” testosterone. Free testosterone and testosterone bound to albumin are easily used by the body—they are also called bioavailable testosterone (Antonio, 2016).
Total testosterone is a measure of both free and bound testosterone.
Testosterone plays a vital role in the following body functions (Nassar, 2022):
- Sex drive
- Growth of facial and body hair
- Getting and maintaining erections
- Producing sperm
- Regulating mood
- Maintaining muscle mass and bone density
- Producing red blood cells
Where does testosterone come from?
As with most hormonal pathways in the body, testosterone production is a bit complex. Here’s the general process:
- A part of your brain called the hypothalamus releases the gonadotropin-releasing hormone (GnRH).
- GnRH tells the pituitary gland to release luteinizing hormone (LH) into your bloodstream.
- In males, once LH reaches the testicles through the blood, it stimulates special cells in the testes, called Leydig cells; these Leydig cells are ultimately responsible for producing testosterone.
- In females, specialized cells in the ovaries called theca cells make testosterone.
- As serum testosterone levels rise, signals are sent to the pituitary gland and hypothalamus to stop stimulating testosterone production.
It’s a complex process, but this feedback loop is the body’s way of trying to keep hormone levels in check.
Why test for free testosterone?
Many men are concerned about their testosterone levels. We know that aging causes a decline in testosterone levels over time, with studies showing that levels start dropping around age 35 and then decline further after age 80 (Handelsman, 2015). But just having low testosterone is not necessarily a problem.
Some people develop symptoms along with their low hormone levels, indicating a testosterone deficiency (also called hypogonadism or low-T). Anywhere from 2-12% of men overall may have a testosterone deficiency. Interestingly, if you look at older men over 80, up to 50% may have low testosterone levels (Zarotsky, 2014; Snyder, 2020).
If you think you may have low testosterone, talk to your healthcare provider and have your levels checked. Be sure to look at both your free and total testosterone levels—many people will check total testosterone, but forget about free testosterone levels. However, free testosterone levels may fall faster than your total testosterone concentration (Snyder, 2020).
Testosterone test kit: how accurate are they?
Some men may have normal total testosterone levels but low free testosterone—so if you only test for one and not the other, you and your provider may not be getting the whole picture (Antonio, 2016).
The most accurate method of testing free testosterone is by a process called equilibrium dialysis; however, this test is time-consuming and not readily available to all providers. Therefore, many tests rely on other markers that help calculate free testosterone levels.
Free testosterone levels
It can be difficult to know what is “normal”—this is especially true for free testosterone. Most of the time, when people are talking about testosterone levels, they are referring to total testosterone.
Normal testosterone levels run in the 300–1000 nanograms per deciliter (ng/dL). This can vary daily and by the time of day, so providers will typically check total testosterone levels between 8 a.m. and 10 a.m. on two different days. Levels below 300 ng/dl are considered below normal (Sizar, 2021).
In contrast, free testosterone is difficult to measure directly. Most laboratories will use an equation to indirectly measure your free testosterone levels based on your total testosterone and other values. Also, the free testosterone “normal range” can vary based on the lab you are using, and different guidelines may recognize different levels for normal ranges of free testosterone.
A general rule of thumb is that free testosterone less than 50–65 picogram per milliliter (pg/mL) is considered low. However, this is often evaluated in the setting of low total testosterone (Trost, 2016).
Sex drive and testosterone: the relationship explained
What can cause low testosterone?
Some conditions that can lead to low testosterone levels include (Sizar, 2021):
- Damage to testes
- Chemotherapy or radiation
- Autoimmune diseases
- Thyroid dysfunction
- Pituitary gland dysfunction
- Medication side effects, especially narcotics and antidepressants
Treating the underlying conditions may lead to a normalization of testosterone levels.
If your testosterone measurements are abnormal, your healthcare provider may want to check additional lab tests like luteinizing hormone, follicle-stimulating hormone (FSH), or dehydroepiandrosterone sulfate (DHEA-S).
What happens if your free testosterone is low?
Even if your total testosterone concentration test results are average, you may still have low free testosterone, which can lead to symptoms of hypogonadism like (Sizar, 2021):
- Decreased sex drive (libido)
- Erectile dysfunction, including loss of morning erections
- Lean muscle mass loss
- Body and facial hair hair
- Fatigue (feeling tired all the time)
- Overweight or obesity
- Bone weakening (osteoporosis)
Consult with your healthcare provider if you think you may have any of these symptoms.
8 ways to naturally boost testosterone
Can you have too much testosterone?
Testosterone needs to be balanced with other hormones. Too little, and you can have hypogonadism. However, having too much is also not good for either men or women.
The most common cause of too much testosterone (androgens) in men is the use of anabolic steroids, like the performance-enhancing steroids that have been associated, unfortunately, with many professional athletes. Too much testosterone in men can cause the following (Ganesan, 2021):
- Increased risk of prostate cancer
- Male breast enlargement (gynecomastia) because some of the excess testosterone gets converted to estrogen
- Sleep apnea
- Aggressive moods
- Elevated blood pressure (hypertension)
- High cholesterol (dyslipidemia)
- Increased red blood cell count (erythrocytosis) and clotting problems
- Shrinking testicles
Other causes of high testosterone in men include testicular or adrenal gland tumors.
In women, polycystic ovary syndrome (PCOS) is the most common cause of high testosterone levels. PCOS is due to an imbalance in the ratio of female to male hormones—the male hormone levels are higher than usual. Women with PCOS typically have irregular menstrual cycles, abnormal hair growth (hirsutism), infertility, acne, weight gain/obesity, and multiple ovarian cysts on ultrasound (Rasquin Leon, 2021).
What are normal testosterone levels?
When to see a healthcare provider
Remember that older men will have lower testosterone measurements than they did in their teens and 20s—this is a normal part of aging. But the number alone is not the issue—it’s whether that number leads to problems.
Your healthcare provider can help you navigate this tricky path by performing a physical exam and ordering blood tests to determine if and why you have low T and whether testosterone replacement therapy is right for you.
- Antonio, L., Wu, F. C., O’Neill, T. W., Pye, S. R., Ahern, T. B., Laurent, M. R., et al. (2016). Low Free Testosterone Is Associated with Hypogonadal Signs and Symptoms in Men with Normal Total Testosterone. The Journal of Clinical Endocrinology and Metabolism, 101(7), 2647–2657. doi:10.1210/jc.2015-4106. Retrieved from https://pubmed.ncbi.nlm.nih.gov/26909800/
- Ganesan, K., Rahman, S., & Zito, P. M. (2021). Anabolic steroids. [Updated Jun. 4, 2021]. In: StatPearls [Internet]. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK482418/.
- Handelsman, D. J., Yeap, B., Flicker, L., Martin, S., Wittert, G. A., & Ly, L. P. (2015). Age-specific population centiles for androgen status in men. European Journal of Endocrinology, 173(6), 809–817. doi:10.1530/EJE-15-0380. Retrieved from https://pubmed.ncbi.nlm.nih.gov/26385186/
- Nassar, G. N. & Leslie, S. W. (2022) Physiology, Testosterone. [Updated Jan. 4, 2022]. In: StatPearls [Internet]. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK526128/
- Rasquin Leon, L. I., Anastasopoulou, C., & Mayrin, J. V. Polycystic ovarian disease. [Updated Jul. 21, 2021]. In: StatPearls [Internet]. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK459251/
- Sizar, O. & Schwartz, J. (2021). Hypogonadism. [Updated Jun. 29, 2021]. In: StatPearls [Internet]. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK532933/
- Snyder, P. J. (2020). Approach to older men with low testosterone. In: Matsumoto, A. M., Schmader, K. E., & Martin, K. A. (Eds.). Retrieved from https://www.uptodate.com/contents/approach-to-older-men-with-low-testosterone
- Trost, L. W. & Mulhall, J. P. (2016). Challenges in testosterone measurement, data interpretation, and methodological appraisal of interventional trials. The Journal of Sexual Medicine, 13(7), 1029–1046. doi:10.1016/j.jsxm.2016.04.068. Retrieved from https://pubmed.ncbi.nlm.nih.gov/27209182/.
- Zarotsky V., Huang, M., Carman, W., Morgentaler, A., Singhal, P.K., Coffin, D. et al. (2014). Systematic literature review of the epidemiology of nongenetic forms of hypogonadism in adult males. Journal of Hormones, 2014, Article ID 19034. doi:10.1155/2014/190347. Retrieved from https://www.hindawi.com/journals/jhor/2014/190347/