Free testosterone, total testosterone and SHBG, explained

What is SHBG?

SHBG (sex hormone-binding globulin) is a protein made by your liver that holds testosterone tightly in the blood. The standard view is that while testosterone is attached to it, your tissues can't use it.¹ In men, about 40 to 50 per cent of circulating testosterone is bound to SHBG, most of the rest is held loosely by albumin and other blood proteins, and only about 1 to 2 per cent floats free.^{1, 4}

Form of testosterone	How it's held	Rough share in men	The usual view
Bound to SHBG	Tightly	40-50%	Not available to tissues while it's bound1
Bound to albumin	Loosely (a weak bond)	Most of the rest	Counted with free testosterone as "bioavailable"6
Free (unbound)	Not held	About 1-2%	Treated as the biologically active form4, 7

Total testosterone, the number on most reports, counts all of it, bound and free.² Free testosterone is only the unbound part. Bioavailable testosterone is free plus albumin-bound.⁶

The "only free testosterone counts" idea is a simplification, though. Healthy Male points out that bound testosterone can also act on cells, in ways that aren't fully understood, and that there's no evidence free testosterone has an effect separate from total testosterone.³

Free vs total testosterone: which one matters more?

For most men, total testosterone is the main number. SHBG, and the free testosterone worked out from it, matter most when the total is borderline or when something is likely to push SHBG unusually high or low.^{4, 5, 7} The more SHBG you have, the more testosterone is bound and the less is free.¹ So two men can have the same total and quite different amounts of free testosterone.

The European Male Ageing Study of 3,334 men aged 40 to 79 showed both sides.²⁰ Men with a normal total but low calculated free testosterone tended to be older and in poorer health, had higher SHBG and reported more sexual and physical symptoms. Men with a low total but normal free testosterone tended to be younger and heavier, had lower SHBG, and didn't show the features linked to low testosterone.²⁰ It's an observational study, so it shows links, not cause and effect. Healthy Male adds a caution: when total is normal and calculated free testosterone is low, the low figure seems to reflect unusual SHBG, and there's no evidence the calculated free level itself causes symptoms.³

What SHBG does to the maths

These are made-up numbers, not a real person's results. We worked them out with the Vermeulen equation,¹⁸ assuming an albumin of 43 g/L.

Total testosterone	SHBG	Calculated free testosterone
14 nmol/L	20 nmol/L	About 370 pmol/L
14 nmol/L	40 nmol/L	About 250 pmol/L
14 nmol/L	60 nmol/L	About 190 pmol/L

Same total, but as SHBG triples the free figure roughly halves. Against Auckland's range for men aged 20 to 50 (218 to 681 pmol/L), the first result sits inside it and the last one falls below it.⁷ A total of 14 nmol/L also sits inside the 7 to 15 nmol/L window where that lab treats the total as not clear-cut on its own.⁷ That's why labs recommend SHBG when the total is low or borderline,⁶ and why the Endocrine Society of Australia says a total near either end of the range should be read alongside SHBG.⁵

How do labs calculate free testosterone?

AU and NZ labs usually calculate free testosterone rather than measure it. They put total testosterone and SHBG, and sometimes albumin, into the Vermeulen equation, published in 1999.^{3, 6, 7, 9, 13} The original study found the calculated figure closely matched equilibrium dialysis, the slow reference method, while direct free testosterone immunoassays and the free androgen index did not.¹⁸

Two caveats. A 2010 study led by researchers at Concord Hospital in Sydney compared five formulae with dialysis in 2,159 samples from men and found the commonly used formulae overestimated free testosterone.¹⁹ And the Endocrine Society of Australia found no evidence that calculated free or bioavailable testosterone is a better measure than total testosterone, noted their ranges are even less well defined, and doesn't recommend them for clinical decision making.⁵ bpac nz, writing for New Zealand GPs in 2024, is more open: it prefers calculated free testosterone over direct assays when doubt remains after two morning total testosterone tests.⁴

The free androgen index (FAI) is a different calculation: total testosterone x 100, divided by SHBG. It isn't reliable in men. Awanui says it can give wrong results in male patients, and Pathology Tests Explained notes that the Endocrine Society of Australia recommends it only for women.^{1, 6}

Do NZ labs need testosterone and SHBG requested together?

Yes, at Awanui. If the form only says testosterone, you get total testosterone and nothing else. Since 17 September 2024, Awanui Labs has offered four testosterone request options:⁶

Request option (code)	What comes back
Testosterone only (TESF)	Total testosterone only. No SHBG, no calculations.
Testosterone + SHBG (FAI)	Total testosterone, SHBG, calculated free testosterone (Vermeulen) and FAI
SHBG (SHB)	SHBG only
Testosterone-LCMS (LCM), specialist only	Total testosterone by mass spectrometry. No SHBG, no calculations.

Awanui leaves the FAI off when total testosterone is above 52 nmol/L or SHBG is below 13 nmol/L, because the calculation becomes unreliable there. Its notice also recommends SHBG whenever total testosterone is low or borderline, particularly in older men and men carrying extra weight.⁶

Health NZ's Auckland hospital lab (LabPlus, Te Toka Tumai) vets these requests. It may decline SHBG or free testosterone for a man whose total testosterone is below 7 or above 15 nmol/L, because the total already gives a clear answer, and adding them needs a chemical pathologist's approval.^{7, 8} bpac nz notes some regions only fund free testosterone when the total is inconclusive (7 to 15 nmol/L) or an endocrinologist recommends it.⁴

Do Australian labs need SHBG to report free testosterone?

In practice, yes. Free testosterone is usually a calculation, so SHBG has to be on the request.³ The Royal Melbourne Hospital lists free testosterone as a calculated value that requires an SHBG order, and Alfred Health calculates it from testosterone, SHBG and albumin.^{11, 13} Medicare lists SHBG and "free or total testosterone" as separate tests in the same hormone item group, with one schedule fee for one test from the group and a higher one for two.^{14, 15} What you pay depends on whether the lab bulk bills.

What is a normal free testosterone range?

There isn't a single one. The AU and NZ hospital labs below publish adult male ranges that run from about 180 to 740 pmol/L, depending on the lab and your age.^{7, 9, 11, 13} Healthy Male notes there's no standardised normal range for free testosterone in Australia,³ so read your result against the range printed on your own report.

Lab	Age	Calculated free testosterone (pmol/L)
Royal Melbourne Hospital (VIC)	Adult men	260-74011
Alfred Health (VIC)	Adult men	260-74013
LabPlus, Health NZ Te Toka Tumai Auckland	20-50 / over 50	218-681 / 179-5207
Canterbury Health Laboratories, Health NZ	20-50 / over 50	220-680 / 180-5209

Alfred Health says its range comes from a study of healthy young men, and that healthy older men can have calculated free testosterone as low as 140 pmol/L.¹³ The NZ labs publish a separate, lower range for men over 50. Auckland's lab notes that free testosterone below 220 pmol/L is significantly associated with sexual symptoms in men, and bpac nz uses the same figure, alongside symptoms, in its guidance for GPs.^{4, 7} Healthy Male points out that this cut-off rests on limited evidence.³ If you've read US sites that quote free testosterone in pg/mL or ng/dL, convert first with our testosterone unit converter.

What is a normal SHBG level for men?

Adult male SHBG ranges sit roughly between 13 and 78 nmol/L, depending on the lab and your age.^{8, 10, 12}

Lab	Age	SHBG (nmol/L)
Royal Melbourne Hospital (VIC)	Adult men	17-7812
LabPlus, Health NZ Te Toka Tumai Auckland	20-49 / 50 and over	13-49 / 15-718
Canterbury Health Laboratories, Health NZ	15-49 / 50 and over	13-49 / 20-7710

SHBG tends to climb with age. Australian researchers who analysed 110,712 blood samples from one large pathology lab found men's SHBG reaches its lowest point at about age 20, stays fairly steady until the sixth decade of life, then rises gradually.²¹ bpac nz notes that this rise is one reason free testosterone falls in older men.⁴ For how total testosterone shifts with age, see testosterone levels by age.

What causes high SHBG in men?

High SHBG in men is linked with ageing, liver disease, an overactive thyroid and some medicines, among other things. Ageing brings a mild rise. Some health conditions and medicines push SHBG up much further.^{4, 5}

• Ageing. A gradual rise in later life.^{5, 21}
• Liver disease, including cirrhosis and hepatitis.^{1, 4, 5}
• An overactive thyroid, and thyroid hormone replacement.^{1, 4, 5}
• Some epilepsy medicines.^{4, 5}
• Smoking. Current smokers had higher SHBG in pooled data from 12,330 men.^{4, 22}
• Anorexia nervosa, HIV, and medicines that contain oestrogen.^{1, 4, 8}

When SHBG is markedly high, total testosterone can read high too, without any sign of extra testosterone activity in the body.⁵ If your SHBG is flagged high, raise it with your GP. Ask whether thyroid or liver tests, or any medicine you take, could explain it.

Does alcohol raise SHBG?

Not clearly, unless the liver is affected. Liver disease raises SHBG,⁵ and Pathology Tests Explained notes that alcoholism and liver disease can lower testosterone in men.² Outside liver disease the link is weak: in the pooled data from 12,330 men, drinking went with higher levels of some other hormones, but showed no clear link with SHBG.²² If you drink heavily and your SHBG is high, raise both with your GP. Don't assume a few beers explains an odd number.

What causes low SHBG in men?

Carrying extra body fat and insulin resistance are two of the main things linked with low SHBG in men. In large studies, higher body mass index goes with lower SHBG,²² and the Endocrine Society of Australia lists obesity, insulin resistance and taking testosterone or other androgens as things that suppress it.⁵ Other causes include type 2 diabetes, an underactive thyroid, and less common conditions such as Cushing's syndrome, acromegaly and nephrotic syndrome.^{1, 4, 8}

Low SHBG can pull total testosterone down while free testosterone stays where it was.³ The Endocrine Society of Australia warns that in men with obesity or insulin resistance, a total testosterone below the range, especially with normal LH and FSH, isn't enough on its own to show a true shortfall of testosterone.⁵ That's the "low total, normal free" group from the European study above.²⁰

Body weight is the factor on this list a man has most say over. A 2013 meta-analysis of 24 studies found weight loss in men with obesity was associated with higher testosterone, both SHBG-bound and unbound, with bigger rises after bariatric surgery than after low-calorie diets.²³ The authors noted that few randomised trials of diet and exercise exist and their results conflict, so read it as a direction, not a forecast for any one man. Our guide to raising testosterone naturally covers what the evidence does and doesn't show.

If your SHBG is flagged low, raise it with your GP, and ask whether blood sugar or thyroid tests make sense for you.

Should you ask your GP to add SHBG?

If your total testosterone is borderline, or something on the lists above applies to you, it's a fair question to ask.^{4, 6} Both countries start with total testosterone taken early in the morning. bpac nz advises a test between 7 and 11am, ideally after an overnight fast, repeated about four weeks later if the result is below range. The Endocrine Society of Australia and Awanui suggest 8 to 10am.^{4, 5, 6} healthdirect says you usually need to fast and should have the test in the morning.²⁴ SHBG needs no special preparation, but it's drawn with testosterone, so follow the testosterone rules.¹

• New Zealand: if your GP uses Awanui, ask about "Testosterone + SHBG" (code FAI) rather than "Testosterone only".⁶ Other labs may word the options differently, and some may decline SHBG if your total is clearly low or clearly normal.⁸
• Australia: ask about testosterone and SHBG, with calculated free testosterone. Labs such as the Royal Melbourne Hospital need the SHBG order to calculate it.¹¹

The full list of markers worth discussing, including LH and FSH, is on our testosterone blood test checklist. Your GP decides what's needed for you.

How much does an SHBG test cost?

In Australia, testosterone plus SHBG has a Medicare schedule fee of A$43.70 (A$30.50 for one test on its own). In New Zealand, a non-funded SHBG test at Canterbury Health Laboratories is NZ$34.83 plus GST, and a self-requested panel that includes SHBG is NZ$104.99 at BODYiQ.^{10, 14, 15, 17}

Prices last checked 30 September 2026.

Country	Route	What's included	Price
Australia	Medicare schedule fee, item 66695	One test from the hormone group, such as testosterone only	A$30.5014
Australia	Medicare schedule fee, item 66698	Two tests from the group, such as testosterone plus SHBG	A$43.7015
New Zealand	Canterbury Health Laboratories, non-funded price (doctor's request needed)	Testosterone or SHBG, per test	NZ$34.83 each, excl. GST9, 10, 25
New Zealand	BODYiQ self-request (Awanui Group)	Total testosterone only	NZ$44.99 incl. GST16
New Zealand	BODYiQ self-request (Awanui Group)	Total and free testosterone, SHBG and FAI	NZ$104.99 incl. GST17

The Medicare figures are schedule fees, not necessarily what you pay. That depends on whether the lab bulk bills. Canterbury Health Laboratories no longer accepts self-requests, so its price applies to a doctor's request that isn't publicly funded.²⁵ Whichever route you use, book an early-morning collection, because testosterone runs highest in the morning.² Teak doesn't sell tests and takes no commission from any lab. A single self-requested result doesn't settle anything: guidance calls for a repeat morning test if the first one is low, and a GP to interpret the results.^{4, 5} For every route side by side, see what a testosterone test costs in Australia and New Zealand.

What should you do with a flagged result?

Take it to your GP. A flagged SHBG or free testosterone is a reason for a conversation, not a verdict. Treatment decisions, including whether testosterone therapy is appropriate, are a doctor's call (see coaching vs TRT). Our safety page explains what we always send to a GP, and who Teak isn't for.

If you want every marker on your panel explained in plain English, that's what the Baseline, 4 weeks is for. Here's how it works. Chatting first costs nothing.

How we research, source and review these guides is set out in our editorial policy.

General information, not medical advice.