Scroll TikTok long enough and someone will tell you your testosterone is “normal” but your “free” testosterone is what’s actually impacting your energy, your gym gains and your sex drive. It might sound like the real answer your GP missed, but it’s not that simple.
Free testosterone is a real thing — it’s the small fraction of testosterone circulating in your blood, separate from the large amount attached to proteins like sex hormone-binding globulin (SHBG) and albumin. But the idea that ‘free’ testosterone is the only part that matters, and that a “normal” total testosterone result is misleading, isn’t the case.
Here’s what you need to know about free testosterone, how it’s measured and whether it matters.
How does testosterone work?
Testosterone is the main androgen (a type of hormone) in men. It drives the physical changes that happen during male puberty, and it regulates sperm production, bone health, muscle mass and sex drive and other psychological functions. It’s important for normal development and overall wellbeing.
The Leydig cells in the testes of adult men produce around 3.5-7mg of testosterone each day. The site of testosterone production ensures high levels in the testes (about 100-times higher than levels in the blood), where the hormone is critical for sperm production. Testosterone from the testes enters the blood, which transports it to other parts of the body where it acts on the brain, muscles, bone and other tissues.
Testosterone is transported in the blood in three main ways. Just under half of the testosterone in the blood is bound to sex hormone-binding globulin (SHBG), more than half is bound to albumin. A small amount — around 2% of total testosterone — is ‘free’ in the circulation, this is called free testosterone. Some is also bound to other proteins in the blood — cortisol-binding globulin and orosmucoid — but this is not well understood and is therefore, unfortunately, largely ignored. Bound testosterone likely acts as a reservoir, helping to stabilise the availability of testosterone in the body.
Free testosterone vs total testosterone
When you have a blood test to measure your testosterone level, it’s the total amount of testosterone that’s measured (all of the ‘bound’ and ‘free’). Measuring free testosterone is technically difficult and there is no standardisation, so it is not normally measured. ‘Free’ testosterone results from blood tests are usually calculations based on equations that include total testosterone levels, SHBG levels and (sometimes inaccurate) estimations about the binding of testosterone to SHBG.
It is widely believed that ‘free’ testosterone is the active form of testosterone, and that the testosterone bound to SHBG and albumin cannot influence the body’s cells. This is a simplistic and incorrect understanding of how testosterone works in the body. There are mechanisms by which bound testosterone affects cells. The fact that these are complicated and not fully understood does not mean they should be ignored (like poor old orosmucoid- and CBG-bound testosterone). Even if ‘free’ testosterone is more available to the body’s cells, that would mean that it’s also more available for metabolism and clearance from the body.
The transport and activity of testosterone in the body are not fully understood. This isn’t because people aren’t smart enough to understand it. We just don’t have all of the information we need to understand these things completely.
Can you have normal total testosterone and low free testosterone?
Yes.
It is possible to have a total testosterone level in the normal healthy range but also have a low level of free testosterone. In these cases, the low free testosterone levels seem to be related abnormal SHBG levels (remember, SHBG levels are one of the variables in the free testosterone calculations); there’s no evidence that calculated free testosterone levels are the cause of symptoms.
The ‘free testosterone hypothesis’ is used by some people to explain why some men seem to experience symptoms of low testosterone, even when the total amount of testosterone in their bodies is within a normal range. The thinking is: if it’s the free amount that really matters, total testosterone levels that are ‘normal’ might be missing a low ‘free’ testosterone level. They argue that the ‘free’ testosterone level is what should be measured.
Can you have low total testosterone but normal free testosterone levels?
Yes.
There’s a case report of a male patient with a genetic mutation that caused an inability to produce SHBG. His ‘free’ testosterone level was ‘normal’ but his total testosterone level was very low. The fact that the man had “normal gonadal development and normal spermatogenesis” is commonly used to support the argument that SHBG is unnecessary for normal function and that it is free testosterone that’s actually important. But he had a history of fatigue, muscle weakness, impaired exercise tolerance, and low body weight. In addition, he experienced trembling muscles during minor exercise and low libido, decreased spontaneous morning erections, fatigue, muscular weakness, decreased shaving frequency, inability to concentrate, sleep disturbance, and depressed mood. These are the very same symptoms that are claimed to be caused by low ‘free’ testosterone, occurring in a man with a ‘normal’ level of ‘free’ testosterone.
What’s a normal range of testosterone?
The normal range for total testosterone is 12-35 nmol/l (350-1000 ng/dl), with values between 8-12 nmol/l considered borderline low and values below the threshold of 6 nmol/l needing treatment with testosterone replacement therapy.
There is no normal range of ‘free’ testosterone that is used in Australia because measurements are not standardised.
When should you get your testosterone tested?
Low testosterone — known clinically as androgen deficiency — can affect energy, concentration and mood. Men may notice persistent tiredness, low motivation, trouble sleeping or feeling sleepy through the day, and a drop in muscle mass and strength alongside weight gain. Sex drive and erection frequency can decline too, and some men report feeling forgetful or low. There symptoms are all non-specific, meaning that they could be caused by a number of health problems, not just a low testosterone level. A doctor may also look for more specific signs of hypogonadism, including small testes, reduced fertility, sparse facial or body hair, and breast tissue changes.
If you’re experiencing symptoms of low testosterone, go to see your doctor. They’ll discuss your symptoms, general health and behaviours, do a physical examination and order further testing if needed. An accurate diagnosis will help you find the right treatment.
Low testosterone treatment
Treatment for low testosterone depends on the underlying cause. Where the testes aren’t producing enough testosterone (primary hypogonadism), testosterone replacement therapy — available as capsules, injections, patches, creams or gels — is the standard and effective treatment. Where the cause sits further upstream, in the hormonal signals from the brain that control the testes (secondary hypogonadism), treatment focuses on addressing that underlying issue, often alongside testosterone replacement. If test results point to androgen deficiency, a GP will typically refer the patient on to an endocrinologist or urologist to confirm the diagnosis and guide treatment. Avoid clinics or centres that advertise treatment for low T or low testosterone.
FAQs
What should my free testosterone be?
There is no evidence based normal range of values of free testosterone. The most recent European guidelines suggest ‘free’ testosterone levels under 220pmol/l should be considered low, despite limited supporting evidence.
What does free testosterone do?
Free testosterone is believed to move easily from the blood into the cells of the body, which is why it’s thought to be the most active form of testosterone in the blood (testosterone bound to SHBG and albumin can interact with the body’s cells, but in different ways). Free testosterone is also cleared more quickly from the circulation (mainly by breakdown in the liver).
Is it good to increase free testosterone?
Our bodies regulate our testosterone levels to maintain homeostasis (a stable and balanced environment within the body even though the external environment and bodily processes are changing). Problems with testosterone levels can have serious consequences for our health, so symptoms should be discussed with your general practitioner and managed by them or another health professional with appropriate expertise, like an endocrinologist (not by following the advice of some bloke on TikTok).
If your total testosterone and SHBG levels are normal, your free testosterone level is probably where it should be. Increasing it further is probably not good.
If your free testosterone level is low because your total testosterone level is low, raising the total level will usually raise free testosterone, which would probably be good.
If your free testosterone level is low because your SHBG level is high (this can be caused by liver disease, high thyroid hormone levels or some antiepileptic therapies), managing health problems or medication could help lower SHBG and raise free testosterone, which would be good.
If your SHBG level is low, which can be caused by obesity, insulin resistance or taking testosterone, your total testosterone level can be reduced without lowering of your free testosterone level. Losing weight can help to raise SHBG and improve total testosterone levels in this situation which would be good.
What happens if free testosterone is low?
Evidence from scientific studies shows that low testosterone levels are associated with symptoms of androgen deficiency (hypogonadism), even in men with testosterone levels in the normal range.
