Free testosterone, total testosterone and SHBG: the difference

The key points

Total testosterone includes bound and unbound hormone. Free testosterone is unbound; bioavailable testosterone also includes the albumin-bound fraction.
Only around 1 to 4 percent of testosterone is free. The rest is bound to SHBG, a protein from the liver, and to albumin.
SHBG controls how large a share of the hormone is free. A high SHBG can hide a deficiency behind a normal total value, and a low SHBG can make a low total look worse than it is.
Total testosterone is the starting point; SHBG and selected additional testing help when the clinical question requires it.
When testosterone deficiency is suspected, the values should always be assessed by a doctor alongside the symptoms.

What is total testosterone?

Total testosterone is the value most people recognise from their reports. It measures all the testosterone in the blood, both the portion bound to proteins and the small portion moving freely. As an overview value it works well, and it is the total value that Swedish reference intervals and clinical guidelines are built on.

At the same time, the total says nothing about how the hormone is distributed. Two men with exactly the same total value can have different amounts of usable testosterone, depending on how much of it sits attached to carrier proteins. That is where the other two values come in.

Free and bioavailable testosterone

Free testosterone is the small fraction not bound to a carrier protein. Bioavailable testosterone conventionally includes both free testosterone and testosterone loosely bound to albumin. The two quantities are not interchangeable.

An appropriate free testosterone measurement or validated calculation can support selected clinical assessments. Its interpretation depends on the method, symptoms and other results; it does not by itself explain tiredness or reduced performance.

What does SHBG do?

SHBG, sex hormone binding globulin, is a protein made in the liver that binds sex hormones tightly. Most bound testosterone sits either on SHBG or, more loosely, on albumin (a common carrier protein in the blood).

The SHBG level therefore decides how large a share of the total is free. SHBG normally rises with age, one reason free testosterone falls faster than the total in older men. Excess weight tends to pull SHBG down instead, and the thyroid, the liver and certain medicines can shift the level in either direction. SHBG is not a hormone itself, but rather the dial that sets how much of the hormone is available.

Why can the total value mislead?

Because SHBG varies from person to person, the same total value can mean different things. Some typical patterns, simplified:

Total testosterone	SHBG	Free share	What it can mean
Normal	High	Low	A deficiency can hide behind a normal total value
Low	Low	Normal	Often no true deficiency
Low	Normal or high	Low	Points more toward true deficiency, investigated further

Swedish clinical guidance makes exactly this point: a low total value alongside a low SHBG need not mean testosterone deficiency, which is why low values are always followed up with SHBG. The table is a simplification and never replaces a doctor's assessment, but it shows why the three values belong together.

Which results are included in the current profile?

Testosterone Basics includes total testosterone, SHBG and albumin. It does not include a separately reported free or bioavailable testosterone analysis or a testosterone/SHBG ratio. These component results can support interpretation, and a clinician can decide whether an additional validated assessment is needed.

The sample is taken fasting at 07:00-10:00 after normal sleep. Symptoms and confirmed low results are needed for diagnosis of testosterone deficiency in men; routine testing of men without symptoms is not recommended.

When should you see a doctor?

See a doctor if you have complaints that suggest hormone deficiency, for example reduced desire, erectile problems, long-standing tiredness or shrinking muscle mass, especially combined with low measured values. Swedish clinical guidance requires symptoms and at least two low morning values before testosterone deficiency is even considered, and the workup involves more values than those described here.

This article explains what the values mean, but interpreting your particular numbers, in your particular context, is always a job for a doctor.

Testosterone Basics includes total testosterone, SHBG and albumin to support interpretation. It does not include a separately reported free or bioavailable testosterone result or a testosterone/SHBG ratio.

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Common questions

What is the difference between free and total testosterone?

Total testosterone includes bound and unbound hormone. Free testosterone is the unbound fraction. Bioavailable testosterone also includes testosterone loosely bound to albumin, so it is a different quantity.

What is SHBG?

SHBG, sex hormone binding globulin, is a protein from the liver that binds sex hormones. The higher the SHBG, the smaller the share of testosterone that is free and active.

What does a high SHBG mean?

A high SHBG means a larger part of the testosterone is bound, so the free share shrinks. The total value can then look normal even though the available hormone is low. SHBG rises with age, among other things, and the thyroid, the liver and certain medicines can also shift the level.

What is the testosterone to SHBG ratio?

It is a calculated index from total testosterone and SHBG. It is not a free testosterone concentration or an interchangeable replacement for a suitable free testosterone assessment in men. Testosterone Basics does not report this ratio.

Is measuring total testosterone enough?

Total testosterone is the initial test. SHBG and selected additional assessment can help with borderline results or relevant symptoms. A clinician chooses the appropriate method; not everyone needs a separate free testosterone result.