SHBG

What is SHBG?

SHBG stands for sex hormone-binding globulin, a protein that is produced primarily in the liver and subsequently released into the bloodstream. The function of SHBG is to bind sex hormones, particularly testosterone and estradiol.

Of all the testosterone and estradiol in your blood, only a small portion is free and directly available to body cells. The majority is bound, about half to SHBG and a large portion to albumin. Only the free, unbound hormone and the portion loosely bound to albumin can penetrate tissues and exert their effect. The hormone bound to SHBG is temporarily inactive.

The amount of SHBG circulating therefore partly determines how much testosterone or estrogen is actually available to your body, independent of the total amount measured.

Why is SHBG measured?

An SHBG test is rarely requested on its own. Usually, the value is combined with a measurement of total testosterone to calculate the free and bioavailable testosterone value. This provides a more precise picture than total testosterone alone, especially when symptoms and lab values ​​do not correspond.

In women, SHBG is regularly included in investigations into hormonal complaints such as irregular cycles, excessive hair growth (hirsutism), or suspected PCOS (polycystic ovary syndrome). In men, the test is relevant in cases of suspected hypogonadism, reduced libido, or unexplained fatigue, where a normal total testosterone value may still be accompanied by a deficiency of free, active testosterone.

SHBG can also provide additional information during the monitoring of thyroid disorders, liver diseases, or weight fluctuations, as all these factors influence the value.

What do abnormal values ​​mean?

SHBG that is too high

An elevated SHBG value causes a larger proportion of your testosterone or estradiol to remain bound and therefore inactive, even if the total amount of hormone is normal. Possible causes of elevated SHBG include:

• An overactive thyroid (hyperthyroidism)
• Liver disease, such as liver cirrhosis
• Use of estrogen-containing medication, such as the contraceptive pill
• Pregnancy
• Underweight or a severely restricted diet
• Aging, especially in men

Symptoms of high SHBG can resemble those of a testosterone deficiency, such as decreased libido or fatigue, even when total testosterone is measured normally.

SHBG that is too low

A decreased SHBG value means that relatively more free, active hormone is circulating in the bloodstream. Possible causes include:

• Overweight or obesity
• Insulin resistance or type 2 diabetes
• An underactive thyroid (hypothyroidism)
• PCOS in women
• Use of androgens or anabolic steroids
• Conditions such as Cushing's syndrome or nephrotic syndrome

In women with PCOS, low SHBG is often associated with relatively high free testosterone, which can contribute to symptoms such as acne, excessive hair growth, and irregular menstruation.

When is it useful to have SHBG measured?

Having SHBG measured is particularly useful when you have symptoms that indicate a hormonal imbalance, while previous blood values ​​such as total testosterone do not provide a clear explanation. Think of persistent fatigue, reduced libido, irregular menstruation, or unwanted hair growth.

An SHBG measurement can also help complete the full picture in the case of existing conditions that affect hormone balance, such as thyroid problems, liver disease, or PCOS. At Zample, you can combine SHBG with testosterone and other hormonal markers, so that a doctor can assess your values ​​in the proper context.