Free vs Total Testosterone and SHBG: What Your Blood Test Is Really Measuring

If you’ve looked at a hormone blood test report, you may have seen more than one testosterone line: “total testosterone”, sometimes “free testosterone” (often marked as calculated), and a protein called SHBG. It’s natural to wonder which number matters.

The short answer is that they work together. This guide explains, in plain English, what each one is, why your doctor looks at them side by side, and how this fits into a careful hormone health assessment in Australia.

Testosterone in the blood: three ways it travels

Testosterone is carried around the body in the bloodstream. Most of it doesn’t float around on its own. Instead, it’s attached to proteins, a bit like passengers on a bus. At any moment, testosterone in your blood is in one of three states:

1. Tightly bound to SHBG. This portion is held firmly and isn’t readily available to tissues.
2. Loosely bound to albumin. Albumin is a common blood protein. Testosterone lets go of it easily, so this portion can become available.
3. Free (unbound). Only a small percentage of testosterone, usually just a few per cent, travels on its own.

Free testosterone plus the albumin-bound portion is sometimes called “bioavailable” testosterone.

What is total testosterone?

Total testosterone is all of the testosterone in your blood added together: the SHBG-bound part, the albumin-bound part and the free part.

It’s the test most often ordered, and it’s the main measurement Australian clinical guidance relies on when assessing testosterone levels. Labs measure it directly, and it’s well standardised compared with the alternatives.

But total testosterone has one blind spot: it can’t tell you how much of that testosterone is tightly held by SHBG.

What is SHBG?

SHBG (sex hormone-binding globulin) is a protein made mainly by the liver. It binds testosterone, and also oestradiol, very firmly.

Think of SHBG as a reservoir. When SHBG is higher, more testosterone is locked up, so total testosterone can look normal even though less of it is readily available. When SHBG is lower, total testosterone can look low even though the available amount is closer to normal.

That’s why an SHBG level is often ordered alongside total testosterone. It gives context to the total figure.

What is free testosterone?

Free testosterone is the small unbound fraction. In practice, most labs don’t measure it directly, because the direct tests are complex and not always reliable. Instead, free testosterone is usually calculated with a formula that uses your total testosterone, SHBG and sometimes albumin.

Here’s the honest part. The Endocrine Society of Australia’s position statement says measuring SHBG can be informative, but it does not recommend using calculated free testosterone on its own for clinical decisions, because the formulas and their reference ranges are less well defined. A calculated free testosterone figure can still help your doctor build a picture, especially when SHBG is unusually high or low. It just isn’t the whole story.

Why your doctor looks at more than one number

No single line on a report answers the question “are my hormones part of the problem?” A doctor puts several things together:

• Total testosterone, the main measurement.
• SHBG, to understand whether the total figure is being pushed up or down.
• Calculated free testosterone, as supporting context where it’s useful.
• LH and FSH, the signalling hormones from the pituitary gland, which help explain why a level might be low.
• Other markers, such as thyroid function, liver function, blood sugar and iron, because these can affect SHBG or cause similar symptoms.
• Your symptoms, history, medicines and goals, which matter as much as the numbers.

For help with the rest of your report, read how to understand hormone bloodwork. If you’re unsure whether your symptoms point to hormones at all, see how to identify low testosterone.

What can affect SHBG?

SHBG levels vary between people and over time. In general terms, things that are commonly linked with higher SHBG include:

• getting older
• an overactive thyroid
• some liver conditions
• some medicines, including certain anti-epileptic and hormonal medicines
• very low body weight or significant under-eating

Things commonly linked with lower SHBG include:

• carrying extra body weight, particularly around the middle
• insulin resistance and type 2 diabetes
• an underactive thyroid
• some hormonal medicines, and past or current use of anabolic steroids

This is general information only. Your doctor will look at your own health history and medicines, and may order further tests if an SHBG reading is unexpected. Please don’t try to change your SHBG on your own based on a single report.

Why testing in the morning, and twice, matters

Testosterone levels follow a daily rhythm. They’re usually highest in the morning and fall later in the day. They also vary from day to day with sleep, illness, stress, alcohol, heavy training and diet.

That’s why:

• Morning collection is recommended, ideally before 10am, and often fasting. Your doctor or the lab will tell you exactly how to prepare.
• One low reading isn’t enough. Australian guidance recommends confirming a low level with a repeat test on a different day before testosterone therapy is considered.

Our testosterone blood test guide covers preparation, collection centres and the two-test rule in detail.

What about women?

SHBG and testosterone matter for women’s hormone health too. Women make testosterone at much lower levels, and SHBG can be influenced by things like thyroid function, body weight, pregnancy and some hormonal medicines, including some forms of contraception and menopausal hormone therapy.

Standard lab tests are less precise at the low levels found in women, and there’s no agreed “low” cut-off. A doctor can talk through your symptoms and decide which tests, if any, are useful for you. A number on a report is never assessed in isolation.

How this fits into OPTIV Health’s process

At OPTIV Health, a telehealth service for hormone health, here’s how blood testing works:

1. Free 15-minute care call. Our care team explains the process and costs. It isn’t a medical consult.
2. A$150 doctor’s consult. An Australian-registered doctor talks with you by phone about your symptoms, history and goals, and decides which tests are appropriate.
3. OPTIV Health’s own blood test panel. OPTIV Health’s standard blood panel includes total testosterone and SHBG, plus organ function, metabolic and general health markers, fifty-plus markers in all. It’s A$229, arranged through OPTIV Health, and usually done twice a year.
4. Two tests before testosterone therapy is considered. These are your two panels for that year, not extra tests. If you’ve had suitable bloods done recently, that report can count as one of the two. Your doctor will confirm.
5. Review. Your doctor looks at every reading together and decides with you what, if anything, is suitable.

OPTIV Health doesn’t charge a monthly subscription. Consults are private, so no Medicare rebate applies. See our cost page for details, or read how to get TRT in Australia for the full step-by-step.

Frequently asked questions

Which is more important, free or total testosterone?

Total testosterone is the main measurement used in Australian clinical guidance. SHBG and calculated free testosterone add context, especially when SHBG is unusually high or low. Your doctor looks at them together, alongside your symptoms. OPTIV Health’s standard blood panel includes total testosterone and SHBG.

Can my total testosterone be normal while my free testosterone is low?

It can happen, often when SHBG is high, because more testosterone is tightly bound. A doctor interprets this in context and may repeat or extend testing before drawing any conclusion.

What does high SHBG mean?

High SHBG means more testosterone is tightly bound. It’s commonly linked with ageing, an overactive thyroid, some liver conditions and some medicines. It isn’t a diagnosis on its own, and your doctor will consider why it might be raised.

What does low SHBG mean?

Low SHBG is commonly linked with extra body weight, insulin resistance and some hormonal medicines. It can make total testosterone read lower, so your doctor interprets the total figure with that in mind.

Do I need two blood tests before starting TRT?

Yes. OPTIV Health requires two separate morning blood tests, on different days, before testosterone therapy is considered. They’re your two A$229 panels for that year, not extra tests, and a suitable recent report from elsewhere can count as one of them.

Is SHBG relevant for women?

Yes. SHBG affects how much testosterone and oestradiol are available in women too. Because testosterone levels in women are low and harder to measure precisely, a doctor decides which tests are useful based on your symptoms.

Get your hormone health checked properly

If you’d like a doctor to look at the whole picture rather than one number, start with a free 15-minute care call. Our care team will explain how assessment and blood testing work and what it costs. Our team is available Monday to Friday, 9am to 7pm Sydney time.

Learn more about testosterone therapy at OPTIV Health.

This article is general information, not medical advice. Speak with a doctor about your own situation.