testosterone

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5 minute read

The difference between total and free testosterone

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Clinical Pharmacist and Copywriter | MPharm

If you’ve ever had a men’s hormone test, you might have seen more than one number on your results. One will say total testosterone. Another might say free testosterone. They sound similar, but they measure different things - and that difference matters.

You could have a “normal” total testosterone level on paper and still feel the classic symptoms of hypogonadism if your free testosterone is too low. That’s why understanding the difference can be the missing piece in getting the right diagnosis and treatment.¹

Total testosterone is the ‘big’ number

Total testosterone is the overall amount of testosterone in your blood at the time of the test.

It includes:¹

Free testosterone: the small fraction your body can use immediately
Bound testosterone: the larger portion attached to proteins, mainly sex hormone-binding globulin (SHBG) and albumin

Think of total testosterone like your full bank balance. It’s everything you have, both the cash you can spend right now and the money that’s tied up in long-term savings.

On average, around 40–50% of your testosterone is bound tightly to SHBG and can’t be used by your body right away. Another 50–60% is bound more loosely to albumin and can be released when needed. The free testosterone, (like your spending money), makes up only about 2–3% of the total.²

Free testosterone is ‘active’

Free testosterone is the testosterone in your bloodstream that’s not bound to proteins. This is the biologically active form that can get to work right away in your tissues.

It’s responsible for:³

Supporting sex drive and sexual function
Building and maintaining muscle mass and strength
Helping with bone density
Maintaining energy and focus
Supporting mood and mental clarity

Understanding the gap

The problem comes when you have a ‘normal’ total testosterone level, but too much of it is tied up with SHBG, leaving little free testosterone available.

High SHBG can happen for several reasons:⁴

Ageing: SHBG naturally increases with age, which means less free testosterone is available despite having a ‘normal’ total testosterone count
Certain health conditions: such as liver disease, hyperthyroidism, or HIV
Medications: like some anti-epileptic or oestrogen-containing drugs

When free testosterone is low, you can experience symptoms of testosterone deficiency even if your total testosterone is “within the normal range.”³

For example, imagine two men both with a total testosterone of 16 nmol/L (which is within the normal range).³

Man A has low SHBG, meaning a healthy amount of free testosterone is available. He feels energetic, has a normal sex drive, and recovers well from exercise.
Man B has high SHBG, so his free testosterone is much lower. Despite the same total number, he feels tired, struggles with muscle recovery, and notices a drop in libido.

If we only looked at their total testosterone, we might miss that Man B is showing signs of low testosterone that need further investigation. This may lead to Man B receiving treatment to help supplement the lack of free testosterone in the body, with the aim to treat symptoms they may be experiencing.

When to check both

For many people, total testosterone testing is a good starting point. But free testosterone testing becomes more important if:¹

Your symptoms suggest low testosterone, but your total result is “normal”
You have a condition or are on medication known to affect SHBG
You’re older and noticing changes in mood, energy, or sexual health
You’re on testosterone therapy, and your clinician wants to fine-tune your dose

The Endocrine Society, the British Society of Sexual Medicine, and other expert guidelines suggest measuring free testosterone when total testosterone is borderline or when SHBG levels may be abnormal.

CTA: Testosterone VBT

Beyond the numbers

One of the big takeaways from the research is that total testosterone alone doesn’t always tell the full story. A 2020 review found that symptoms and outcomes often correlate better with free testosterone than total levels in certain situations, particularly when SHBG is altered.⁵

That means testing both can help your clinician make a more accurate diagnosis, avoid over- or under-treating, and tailor a treatment plan that’s right for you.

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The numan take

If your symptoms don’t match your lab results, ask about checking your free testosterone. It could be the missing clue that explains why you’re not feeling your best, and it could be the first step towards a plan that works for you.

References

^{Liu Z, Liu J, Shi X, Wang L, Yang Y, Tao M, et al. Comparing calculated free testosterone with total testosterone for screening and diagnosing late-onset hypogonadism in aged males: A cross-sectional study.}^{Journal of clinical laboratory analysis}^{. 2017;31(5).}
^{Yang Q, Li Z, Li W, Lu L, Wu H, Zhuang Y, et al. Association of total testosterone, free testosterone, bioavailable testosterone, sex hormone-binding globulin, and hypertension.}^Medicine^{. 2019;98(20): e15628.}
^{Lolck KV, Alcazar J, Kamper RS, Haddock B, Hovind P, Dela F, et al. Compared to total serum testosterone, calculated free testosterone has a stronger association with lean mass, muscle strength, power, and physical function in older men.}^{Aging clinical and experimental research}^{. 2025;37(1): 203.}
^{Gyawali P, Martin SA, Heilbronn LK, Vincent AD, Jenkins AJ, Januszewski AS, et al. Higher serum sex hormone-binding globulin levels are associated with incident cardiovascular disease in men.}^{The journal of clinical endocrinology and metabolism}^{. 2019;104(12): 6301–6315.}
^{Winters SJ. SHBG and total testosterone levels in men with adult onset hypogonadism: what are we overlooking?}^{Clinical diabetes and endocrinology}^{. 2020;6(1): 17.}

Written by Hassan Thwaini

Clinical Pharmacist and Copywriter, Master of Pharmacy (MPharm)

Hassan is a specialist clinical pharmacist with a background in digital marketing and business development. He works as a Clinical Copywriter at Numan, leveraging his research and writing abilities to shine a light on the health complications affecting men and women.

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testosterone

3 minute read

What is the AMS scale and how does it help diagnose low testosterone?

What is the AMS scale and how does it help diagnose low testosterone? It’s a bit of a paradox: low testosterone is easy to identify, yet millions of men in the UK are going undiagnosed every year. One of the reasons why is that many men simply don’t know the symptoms of testosterone deficiency (TD). The AMS scale is helping to bridge that knowledge gap. It’s a simple way of finding out whether you have symptoms consistent with TD, allowing you to follow up on your results and take better control of your health. Here’s all you need to know about the questionnaire and how it can help to diagnose TD. What is the AMS scale? The Aging Males' Symptoms (AMS) scale is a set of 17 questions that help to identify a testosterone deficiency. You’re presented with a range of symptoms (e.g. sleep problems) and asked to rate their seriousness from 0 (none) to 5 (severe). You’ll get a total score out of 85. A score of 26 or under means you have no significant symptoms consistent with a low testosterone level. 27-36: you have mild symptoms consistent with a low testosterone level. 37-49: you have moderate symptoms consistent with a low testosterone level. Over 50: you have severe symptoms consistent with a low testosterone level. Of course, a high score alone doesn’t necessarily mean you have TD. But if your test does throw up some unexpected results, your next step should be a blood test to confirm the results of the questionnaire. Who is it aimed at? Despite the name, the AMS scale is relevant for men of all ages. Your testosterone levels start to decrease by around 1% a year once you hit your 30s. However, that doesn’t mean TD is limited to over 30s. It can affect younger men too, so the questionnaire is still worth taking if you have a few unexplained symptoms that you can’t get to the bottom of. Which questions does it ask? The AMS scale lists 17 symptoms related to low testosterone levels. You just have to rate the impact of each one. Here is the full list of symptoms in the questionnaire: Decline in your feeling of general wellbeing Joint pain and muscular ache Excessive sweating Sleep problems Increased need for sleep, often feeling tired Irritability Nervousness Anxiety Physical exhaustion / lacking vitality Decrease in muscular strength Depressive mood Feeling that you have passed your peak Feeling burnt out, having hit rock-bottom Decrease in beard growth Decrease in ability/frequency to perform sexually Decrease in the number of morning erections Decrease in sexual desire/libido What are the benefits of the questionnaire? The main aim of the test is to help diagnose a testosterone deficiency. However, there are plenty of other benefits: You can start to join the dots between different symptoms to see if there’s a pattern and underlying cause It quantifies your health issues, allowing you to put a number on things and making it easier to track concerns over time It helps to detect health concerns early on, meaning you can act on unusual results before they become a bigger problem Having a set of results to refer to makes it easier for some men to discuss sensitive issues with their doctor Can the AMS scale diagnose TD? No. Although your AMS results can indicate a testosterone deficiency, only a blood test can tell you for sure whether or not you have one. To confirm a diagnosis of testosterone deficiency, you need to take two tests spaced at least two weeks apart. This is because your testosterone levels fluctuate naturally, so two tests can confirm whether you have consistently low testosterone and can also help to identify a baseline from which to work from. That being said, the questionnaire is generally seen as a good indicator of TD. One study found that it was a reliable way of identifying early symptoms and then monitoring the effectiveness of follow-up treatments. What should I do if my results indicate a potential testosterone deficiency? If you get a score of 27 or more on the AMS scale, it’s recommended that you measure your testosterone levels with a Venous Blood Test (VBT), known as the gold-standard for accuracy and reliability. If the blood test confirms the results of the questionnaire, your next step is to discuss treatment options with a clinician. They may recommend testosterone replacement therapy (TRT), lifestyle changes, symptom management, or weight loss to restore your levels to normal. The numan take The Ageing Males’ Symptoms (AMS) scale is a set of 17 questions that help to identify if you may have testosterone deficiency. Beyond that it can also help you track your health over time, and empower you to make better decisions for your long-term wellbeing. The questionnaire alone can’t diagnose a testosterone deficiency, but it’s a vital first step to identifying and correcting one.

testosterone

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Why do so many men get misdiagnosed with depression when they have low testosterone?

There's been a surge in interest in men's mental health in recent years, and all for good reason too—we want our fellow men to speak up. Yet, as awareness grows, so too does the propensity for misdiagnosis. Many non-specialist physicians are quick to diagnose depression without a deeper investigation into the biochemical roots of distress.

testosterone

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If you've ever done a blood test, you've likely come across two key indicators of testosterone levels: total and free testosterone. But what sets them apart? Let's delve into the details.