SHBG Levels Explained: High and Low SHBG

Sex hormone binding globulin (SHBG) is a protein made by the liver. It binds tightly to testosterone, oestradiol and DHT in the blood and holds them in an inactive form. Only the unbound, or free, part of these hormones can act on your tissues.

That makes SHBG essential for reading a testosterone result. Two people with the same total testosterone can have very different amounts of active hormone if their SHBG differs. This guide explains SHBG ranges, what high and low results mean for men and women, how the free androgen index is calculated, and when to see a GP.

Test it in Chiswick: our SHBG blood test costs £49, with your result explained in person by a practitioner. No GP referral needed. Book this test or call 020 4515 0000. Prefer to test at home? A home finger-prick kit is also available, ask us when you enquire.

Quick answer

SHBG ranges vary between laboratories and differ for men and women. One NHS laboratory quotes 19 to 145 nmol/L for women under 50 and 15 to 64 nmol/L for men under 50, with slightly different ranges over 50. Low SHBG is linked with obesity, high insulin, an underactive thyroid and PCOS, and leaves more testosterone free. High SHBG is linked with ageing, an overactive thyroid, liver disease, pregnancy and oestrogen, including the combined pill, and leaves less testosterone free.

What is SHBG?

SHBG acts like a carrier and a reservoir for sex hormones. When SHBG is high, more testosterone is bound and less is free. When SHBG is low, more testosterone is free, even if the total testosterone figure looks ordinary. Androgen and oestrogen levels themselves influence how much SHBG the liver makes, so SHBG both affects and reflects your hormone balance.

SHBG, free testosterone and the free androgen index

Laboratories use SHBG to estimate how much testosterone is available to the body:

• Free androgen index (FAI): total testosterone divided by SHBG, multiplied by 100. It is used mainly for women with suspected androgen excess. One NHS laboratory quotes an FAI range of 0.18 to 7.1 for women under 50 and 0.1 to 5.0 over 50. NHS laboratories note that the FAI is not appropriate for men.
• Free testosterone: for men, free testosterone is usually calculated from total testosterone, SHBG and albumin, which is more reliable than the FAI.

For more on the hormone itself, read our guides to testosterone levels in men and testosterone levels in women.

What your SHBG result means

Ranges below come from NHS laboratories and are a guide only. Always check the range on your own report.

• Low (below the laboratory range, for example under about 15 nmol/L): more testosterone is free. In women this can go with acne, excess hair growth and irregular periods, and is common in PCOS. In men it is often linked with excess weight and insulin resistance.
• Within range: about 19 to 145 nmol/L for women under 50 and 15 to 64 nmol/L for men under 50 at one NHS laboratory. Another NHS laboratory quotes 14.7 to 122.5 nmol/L (women) and 16.2 to 68.5 nmol/L (men) for ages 19 to 49.
• High (above the laboratory range): less testosterone is free. In men this can explain symptoms such as low libido or erectile problems even when total testosterone looks normal. In women it is common with the combined pill or oral HRT.

Causes of low SHBG

NHS laboratories list the following among the causes of low SHBG:

• Obesity and high insulin levels (insulin resistance)
• An underactive thyroid (hypothyroidism)
• PCOS (now also called PMOS), hirsutism and other states of androgen excess
• Medicines such as androgens (including testosterone and anabolic steroids), glucocorticoids and progestins
• Growth hormone excess (acromegaly), and inherited low SHBG in some families

Causes of high SHBG

• Ageing, particularly in older men
• An overactive thyroid (hyperthyroidism)
• Liver disease, including cirrhosis
• Oestrogens, including the combined contraceptive pill, and some anti-epileptic medicines
• Pregnancy, which raises SHBG markedly
• Anorexia, androgen deficiency, high prolactin and growth hormone deficiency

Symptoms that can go with abnormal SHBG

SHBG itself does not cause symptoms. Symptoms come from the change in free hormone levels or from the underlying cause, such as thyroid or liver problems. Women with low SHBG may notice acne, oily skin, unwanted hair growth or irregular periods. Men with high SHBG may notice low sex drive, erectile problems or reduced energy.

When to see your GP

Book a GP appointment if you have:

• excess hair growth that appears quickly, a deepening voice or periods that stop
• erectile problems or low libido that last more than a few weeks
• signs of an overactive thyroid, such as a racing heart, weight loss and feeling hot and shaky

Ask for an urgent GP appointment or call NHS 111 if your skin or the whites of your eyes turn yellow, which can be a sign of a liver problem. Call 999 for chest pain or sudden severe symptoms.

Who might consider an SHBG test?

• Women investigating acne, hirsutism or irregular periods, alongside testosterone
• Men whose symptoms suggest low testosterone but whose total testosterone looks normal
• Anyone on testosterone therapy or hormonal contraception who wants the full picture of their hormone results

Preparing for your SHBG test

• Biotin: NHS laboratories ask anyone taking high-dose biotin (more than 5 mg a day) to have blood taken at least 8 hours after the last dose.
• Medicines: tell us about the pill, HRT, thyroid medicines, steroids and testosterone, as all can shift SHBG.
• Timing: if testosterone is measured at the same time, follow the timing advice for testosterone in our guides and your booking confirmation.

How often to retest

SHBG is usually rechecked only when it will change a decision, for example after starting or stopping hormonal contraception, after thyroid treatment, after significant weight change, or during testosterone therapy as your doctor advises.

Frequently asked questions

Is an SHBG of 15 nmol/L low?

For a woman it is below one NHS laboratory's range of 19 to 145 nmol/L. For a man it sits at the bottom edge of the range at that laboratory. What it means depends on your testosterone level and symptoms.

Is high SHBG bad?

Not on its own. It is common with the pill, pregnancy and ageing. It matters when it lowers free testosterone enough to cause symptoms, or when it points to a thyroid or liver problem.

What does low SHBG mean in women?

More testosterone is free to act, which can contribute to acne and excess hair growth. Low SHBG is common in PCOS and with excess weight and insulin resistance.

Does the contraceptive pill raise SHBG?

Yes. Oestrogens, including the combined pill, raise SHBG. Tell your practitioner if you take it so your result is read in context.

Why is SHBG measured with testosterone?

Total testosterone includes hormone bound to SHBG. Knowing SHBG lets your practitioner estimate the free, active testosterone through the free androgen index or calculated free testosterone.

SHBG testing in Chiswick

Omnia Lifestyle is at 8 to 9 Bedford Corner, The Avenue, Chiswick, London W4 1LZ, a short walk from Turnham Green station on the District line (Piccadilly line trains stop there early morning and late evening only). Buses 94, E3 and 272 stop nearby, and limited parking is available on request when you book. Your sample is taken at the clinic and analysed at the Randox accredited laboratory. Every test price includes a practitioner review of your result with you and a GP feedback report on request. You do not need a GP referral, and most results are ready within a few working days.

Book the SHBG test on its own, or choose the Free Androgen Index test, which adds testosterone and albumin. Men can choose the Testosterone Check, which includes free testosterone. You can also compare every blood test and price, or read our guides to testosterone in men and testosterone in women.

This article is general information, not medical advice. Discuss your results with your GP or practitioner.