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HBG is short for sex hormone binding globulin and it is a serum blood test that can give you valuable insight into your hormones!

Low levels of SHBG may be associated with low thyroid function and low estrogen status while high levels may bind up testosterone leading to weight gain, depression, and other symptoms.

Most physicians don’t put a lot of emphasis on this lab test but it is critical to understanding what is happening with the hormones in your body.

Learn how to understand your lab results, but more importantly what to do about changes to your SHBG.

We will discuss high levels, and low levels, and what to do about both:

Sex Hormone Binding Globulin – Why it is important
So what is SHBG?

SHBG stands for Sex Hormone Binding Globulin.

And it does exactly what it sounds like it does – binds up sex hormones.

But why is this important?

In order to understand we need to talk about some basic physiology.

First, you need to know that hormones float around in your serum in 2 major forms:

#1. Bound to proteins (1) -> the binding of hormones to certain proteins leaves them INACTIVE.

If a hormone is bound to a protein it is NOT available for use.

Consider this like hormones that your body “stores” for later use, similar to you putting food in a deep freezer.

#2. Free and active -> if a hormone is not bound to a protein it is considered “free” and can actually enter into cells and do its job.

Free hormones (such as “free t4” or “free testosterone”) can turn on cellular function and promote genetic changes.

*Side note: this reasoning is why it’s so important to check your free thyroid hormones if you have hypothyroidism. Checking “total t3” or “total t4” has less clinical utility than the free hormones!

SHBG over time in women
You can consider the free hormones as the ACTIVE hormones and the more clinically useful measurement of almost all hormones.

The amount of “free” hormone is usually a VERY small percentage when compared to the “bound” hormone in your blood.

Your body uses this binding system as a way to regulate certain hormones and keep everything in balance or in check.

So where does SHBG fit in?

Sex hormone-binding globulin acts as a binding hormone which means that it may be helpful to think of SHBG as a way to inactive hormones floating around in your serum.

For this reason, you can consider SHBG to be a “Goldilocks” type of protein, meaning you don’t want too much but you also don’t want too little – you need just enough.

Small changes to SHBG levels can bind up free hormones and result in serious symptoms.

It also has a strong affinity (meaning it likes to bind) to certain sex hormones.

It will preferentially bind to hormones in this way:

Preference on dihydrotestosterone or DHT (2) (this is the most potent androgen), then testosterone, then androstenediol, then estradiol, then estrone.

You will notice that SHBG prefers to bind to and inactivate the various androgens in the body.

This is very important because of how this impacts androgens and therefore symptoms in both women and men.

High SHBG will bind up and INACTIVATE both testosterone and DHT meaning that both men and women may start to experience the symptoms of low testosterone (weight gain, depression, loss of muscle mass, irritability, etc.).

While low levels will leave more testosterone ACTIVE meaning that women may start to experience the symptoms of high testosterone (facial hair growth, weight gain, PCOS, irritability, acne, etc.).

What’s worse is that most physicians don’t even test for SHBG even though they understand the difference between “free” and “total” hormone concentration in the blood.

This makes SHBG a VERY important test to ask for if you are experiencing hormone any hormone imbalance as it may shed light on your current problem.

What Causes Increased SHBG?
SHBG is influenced by 2 major hormone systems in the body:

#1. Thyroid hormone (3) and…

#2. Estrogen levels (4).

Both of these hormones may stimulate or INCREASE the circulating amount of sex hormone-binding globulin in the serum.

So what does that mean for you if you have high SHBG?

If you are a woman and you have high SHBG the most likely cause is excessive estrogen use.

This can be either from a condition known as estrogen dominance – meaning you have too much estrogen in your serum.

Or because you are taking birth control (5) or some other form of exogenous hormones.

If you are taking OCP or other hormones and it is causing excessively high levels of SHBG you should take caution!

Increasing your SHBG will influence the amount of free testosterone in your serum and may be one of the reasons that women on OCP tend to gain weight and experience mood changes (6).

Another cause of high SHBG is excessive thyroid hormone replacement therapy.

This is most often seen in those who are taking T3-containing medications (T3 has a direct influence on hepatic SHBG production) like natural desiccated thyroid hormone or liothyronine/cytomel.

It can also occur in those taking T4 medication such as Levothyroxine, but this is less common.

Assessing SHBG accurately in menstruating women can be difficult, though, as women may commonly present with both excess estrogen and hypothyroidism.

If you are taking thyroid

I started a few weeks ago, great minds think alike. I too have the same effect. It also has a very weak anti E effect