Summary

• Sex hormone binding-globulin (SHBG) helps control the amount of sex hormones that are actively working in your body.
• It is a protein made by your liver that attaches to the sex hormones, such as testosterone and oestradiol, in your blood.
• When it does this, your tissues are unable to use these hormones.
• Measuring SHBG shows how much free active sex hormone is available for your body to use.
• A free androgen index is calculated from these results and is valuable in diagnosing hypogonadism (males and females) and polycystic ovary syndrome (females) among other disorders.
• If you have tests to check hormones levels, especially testosterone, your doctors will very often order an SHBG test at the same time in case the results show whether these calculations are needed.

What is sex hormone binding-globulin (SHBG)?

Sex hormone binding-globulin (SHBG) helps control the amount of sex hormones that are actively working in your body. If you have tests to check hormones levels, especially testosterone, your doctors will very often order SHBG tests at the same time in case your results show that a free androgen index calculation is needed.

Testosterone (male sex hormone) and oestradiol (female sex hormone) are in your blood in active and inactive forms. SHBG is a protein that attaches to testosterone and oestradiol in your blood. When it does this, your tissues are unable to use these hormones. These are called bound hormones. Only sex hormones that are not bound to proteins can act on your tissues. These are called free hormones.

High levels of SHBG means that more testosterone is bound and therefore there will be less free testosterone available to act on the tissues.

Low SHBG levels means more testosterone is available to act on the tissues because it is not bound to proteins.

In males, 40-50 per cent of testosterone is bound to SHBG and most of the rest is bound to other proteins. Only a tiny amount is free testosterone and available to act on tissues.

In females, oestradiol increases the amount of SHBG made by the liver. With higher SHBG levels than males, most of the low amount of testosterone binds to this protein. This means that even small changes to SHBG levels in females can result in significant changes in the free testosterone.

In adult men, SHBG levels are normally stable and get higher with age while testosterone levels fall. In postmenopausal women, SHBG, testosterone and oestrogen levels decrease as the ovaries make lower levels of hormones

Your SHBG levels are affected by:

• Age
• Sex
• Levels of testosterone and oestradiol
• Certain conditions such as liver and thyroid disease

Why get tested?

In most situations, if you are being investigated for the causes of a low or high testosterone level, your doctors will order a total testosterone test. This measures all testosterone in your blood and does not distinguish between bound and free testosterone.

In many cases, doctors feel that testosterone provides sufficient information. SHBG is ordered primarily when testosterone results do not seem to be consistent with clinical signs. Testosterone and SHBG levels may be requested to investigate:

Men

• causes of infertility
• decreased sex drive
• erectile dysfunction

Women

• amenorrhoea or absence of menstrual periods
• infertility
• acne
• hirsutism (excessive hair growth)

Having the test

Sample

Blood

Any preparation?

None

Your results

Reading your test report

Your results will generally be presented along with those of your other tests on the same form. You will see separate columns or lines for each of these tests.

When testosterone and SHBG are measured together in females, the laboratory will usually estimate the amount of free testosterone. Measuring free testosterone directly in females is difficult due to the low concentrations of free testosterone in the blood. Instead, an estimation can be done using a mathematical formula such as the Vermeulen equation which uses total testosterone, SHBG and albumin results, or by dividing the testosterone result by the SHBG result to give what is called the Free Androgen Index (FAI):

• FAI = Total testosterone/SHBG x 100.

The Endocrine Society of Australia has recommended that the FAI is only used when testing women. The FAI is not considered a reliable measure in men.

Reference Intervals

Your results will be compared to reference intervals (sometimes called a normal range).

• Reference intervals are the range of results expected in healthy people
• When compared against them your results may be flagged high or low if they sit outside the range.
• Reference ranges may vary between different age groups.
• Reference intervals may vary between labs so only those results that are standardised or harmonised across most laboratories are given on this website.

If your results are flagged as high or low this does not necessarily mean that anything is wrong. Your doctor needs to take your medical history to help interpret your result.

Any more to know?

SHBG concentrations are normally high in children of both sexes. After puberty, SHBG levels decrease more rapidly in males than in females.

Questions to ask your doctor

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods, medications or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

More information

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

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