Measuring testosterone properly: total, free and SHBG

Why a single total value can mislead

Anyone searching for a testosterone test usually finds a single number: total testosterone. It is a reasonable starting point, but it does not answer the question most people are actually asking, which is how much testosterone the body can really use.

The reason is that nearly all testosterone in the blood is bound to proteins. The largest share is held tightly by SHBG (the protein that binds sex hormones) and is then unavailable to the body's tissues. Another share is loosely bound to albumin (a carrier protein in the blood) and can be released when needed. Only a few percent circulates completely free, and it is primarily this free portion that is directly at work in muscle, brain and other tissues.

This means two men with exactly the same total value can have completely different amounts of working hormone. If one has high SHBG, a larger share of his testosterone is locked away; if the other has low SHBG, a larger share is free. Symptoms such as tiredness, reduced drive or slower recovery track the available portion in practice, rather than the headline total.

A total value within the reference range can therefore hide a low free level, and a total value just under the limit can turn out to be less alarming than it looks. Anyone who wants an answer they can trust needs to measure the whole picture: total testosterone, free (bioavailable) testosterone and SHBG together. The reported free value is a calculation that estimates how much of the hormone is actually biologically available to the body. The rest of this guide covers what each part adds and how the sample should be taken.

SHBG: the protein that decides how much is free

SHBG is made in the liver, and the level varies widely between individuals and across life. That variation is what makes the total value so hard to interpret on its own.

Some things push SHBG up. The level rises gradually with age, which has a practical consequence: an older man can keep a normal total value while his free (bioavailable) testosterone falls, because an ever larger share is being bound up. An overactive thyroid, low body weight and certain medicines can also raise SHBG.

Other things push SHBG down. Overweight and insulin resistance (the body's cells responding more sluggishly to insulin) are the most common, and an underactive thyroid can contribute. A man carrying weight around the middle can therefore show a total value that looks low while his free level is less affected, because the low SHBG leaves a larger share free.

This is exactly why SHBG should always be measured together with testosterone. Without the SHBG value it is impossible to tell whether a low total reflects a genuine shortage or mainly a low carrier protein, or whether a normal total is hiding a locked away, low free level. Albumin is measured for the same reason: it is the other binding partner, and the value is needed when the free level is calculated. Albumin itself rarely surprises anyone, but it makes the calculation more honest.

Free (bioavailable) testosterone and the ratio: how the values fit together

Free (bioavailable) testosterone is the share of the hormone that is not tightly bound and can therefore act in the tissues. The reported value is calculated from total testosterone, SHBG and albumin, an established method that estimates the biologically available amount. Measuring the free portion directly is technically demanding, and calculation is the route most laboratory methods and guidelines rely on.

Alongside the calculated free level, the ratio between testosterone and SHBG is often used as a simple index of how much of the hormone is available. The ratio captures the same thing from another angle: a low total with low SHBG can produce a perfectly normal ratio, while a normal total with high SHBG can produce a low ratio that explains symptoms the headline number could not.

A complete testosterone measurement therefore has five parts that are read together: total testosterone, free (bioavailable) testosterone, SHBG, the ratio between testosterone and SHBG, and albumin. Together they answer three questions a single value cannot: how much hormone there is in total, how much is actually available, and why those two numbers differ.

That last question is often the most valuable one. A low free value with high SHBG points to binding as the explanation, while a low free value with normal SHBG points to production itself. The two trails mean different things and are followed up in different ways.

Total and free (bioavailable) testosterone, SHBG with ratio and albumin are collected in Male Hormone Test Base, taken without a referral whenever it suits you.

How to take the sample so the value can be trusted

Testosterone is a moving target, and a carelessly taken sample can give a misleading answer no matter how many values are measured. A few simple rules make a large difference.

Take the sample in the morning, ideally before ten. Testosterone follows a daily rhythm with a morning peak and lower levels through the afternoon and evening, most clearly in younger men. An afternoon sample can look low for entirely natural reasons. Some guidelines also favour fasting samples, since a meal can temporarily lower the level somewhat; a morning draw before breakfast solves both at once.

Pick an ordinary day. Acute illness, even a cold, can temporarily lower testosterone, as can a night of very little sleep, a period of heavy stress or an unusually hard training session the day before. If any of these apply, it is better to wait a few days than to measure a value that mostly reflects the circumstances.

And most important of all: draw no conclusions from a single low value. Levels vary from day to day, and established guidelines require at least two low morning values on separate occasions before testosterone deficiency is even discussed. A low result is a reason to measure again under better conditions, not a verdict in itself. The same holds in reverse: a normal value on a bad day probably understates your true level.

Reading the result, and when to see a doctor

A testosterone result is always read in context. Reference ranges are wide, vary with age and between measurement methods, and where in the range an individual man feels well differs. The values only become meaningful next to how you actually feel: energy, drive, mood, sleep and recovery.

If free (bioavailable) testosterone is low on repeated morning measurement and you have symptoms alongside, it is time to see a doctor. The doctor can then move on to the values that explain why the level is low, above all LH (the pituitary's signal to the testes) and sometimes prolactin. Low testosterone with high LH points to the testes themselves, while low testosterone with low or normal LH points to the signal from the brain. The two trails are investigated differently, and that judgement belongs with a doctor.

At the same time, several of the most common causes of depressed levels can be influenced. With overweight, weight loss can raise testosterone noticeably, and sufficient sleep and regular strength training are associated with better levels, even if the effects on the hormone value itself are usually moderate. Alcohol in larger amounts and certain medicines pull the other way.

What is never the right path is starting testosterone treatment on your own initiative based on a test result. Treatment is a doctor's decision that requires an established cause and follow up, and it affects the body's own production and fertility among other things. A well measured baseline, taken correctly and measured in full, is on the other hand always a good foundation, whether the next step is a doctor's appointment, changed habits or simply a new measurement in a year.

This article is general health information, not medical advice and not an assessment of your values. If you have symptoms or concerns, contact your healthcare provider.