SHBG: what is it and what does your level mean?

SHBG, what is it exactly? Those four letters stand for sex hormone binding globulin. In Dutch it is called geslachtshormoonbindend globuline.

It is often called a hormone, but that is not correct. SHBG is a protein that binds hormones, not a hormone that sends a signal of its own. Your liver makes it and releases it into your blood.

The taxi comparison helps most here. SHBG binds testosterone and oestradiol and drives them through your blood. Testosterone is held tightly, oestradiol far more loosely.

While a hormone is bound, it cannot enter your cells. Only the free part does any work in your tissue. Your total testosterone adds everything together, bound and free.

Your free testosterone is the small part that is actually available at that moment.

Results are reported in nanomoles per litre, written nmol/l. The reference values below are split by sex and by age.

That split by age is not a detail. SHBG rises in men as the years pass. The upper limit therefore moves from 54.1 to 76.7 nmol/l.

That is a difference of more than forty per cent. A man of sixty with an SHBG of 70 sits comfortably inside his own band. Held against the band for a thirty-year-old, he would look too high.

It works the other way too. An SHBG of 19 looks normal, yet his floor is 20.6 nmol/l. So always read the row that matches your own age.

One more thing about these figures. Reference values are not the same at every laboratory or on every machine. Behind us sits a network of independent, certified laboratories.

They do not all measure on the same analyser, and that shifts the bands. If your own report shows a different band, that is the one that counts for you. Never compare a result from one lab against the band of another.

This is the heart of the value. Your total testosterone can mislead you, and it does so in both directions. A low SHBG pulls your total testosterone down while your free testosterone stays perfectly normal.

On paper it looks like a shortfall, yet functionally little is wrong. A high SHBG does exactly the opposite. It props your total testosterone up while the free part falls.

Your result then looks reassuring while you still have complaints.

Here is a common example. You have your testosterone measured at a routine check-up. The result comes back on the low side and that worries you.

If your SHBG turns out to be low as well, part of that low figure is explained. Your free testosterone may be entirely fine. Without the SHBG beside it you would miss that explanation and stay worried for nothing.

What pushes SHBG down? The biggest cause is too much insulin in your blood. That goes with excess weight and insulin resistance, and it is by far the most common reason.

Type 2 diabetes lowers your SHBG too. An underactive thyroid and fatty liver disease, also called NAFLD, count as well. Finally, prednisone and similar medicines lower it, as do androgens and anabolic steroids.

And what pushes it up? Getting older is the most ordinary reason, certainly in men. An overactive thyroid, liver cirrhosis and anorexia also raise your SHBG.

Long-term severe under-eating does the same. Oestrogens you swallow count too: the combined pill and oral hormone therapy. If you take oestrogen through the skin, that effect does not occur.

A patch or a gel does not raise it. Some epilepsy medicines raise your SHBG as well.

SHBG also says something about your metabolism. In large population studies, people with a low SHBG developed type 2 diabetes more often. That link has been seen in men and in women and it is well supported.

Pay close attention to what this does and does not mean. It is an association across groups of people. It is not a prediction about you personally.

A low SHBG is therefore a good reason to have your blood sugar looked at too. It says nothing more than that.

So what do you do with this in practice? Never request SHBG as a standalone value. Put it on the request together with your total testosterone.

Your free testosterone is calculated from that pair, and that is the figure that counts. Measuring only your total testosterone is exactly how a misleading result comes about.

When should you have your SHBG measured? Usually not as a standalone test. You request it when you are having your testosterone measured, for example at a routine check-up.

Or you already have a result from your doctor and it raises questions. That second situation is the most common reason.

There is one rule you really should remember. SHBG belongs on the request together with your total testosterone. Your free testosterone is calculated from those two figures, usually with your albumin as well.

Request total testosterone alone and you miss exactly the context you need. That goes wrong most often in men carrying extra weight and in women using the pill. Our free testosterone test already puts those three values together.

You do not need to fast for SHBG. No fixed time of day is required for this value either. If your testosterone is measured in the same draw, do test in the morning.

Testosterone runs highest in men in the morning and drops afterwards. That way the whole set stays properly comparable.

In women there is something extra at play. If you use the pill or oral hormone therapy, your SHBG is higher because of it. That is not an error in the measurement but a known effect.

So mention it when you request the test, and your result will be read correctly. Never stop a prescribed medicine yourself to get a nicer-looking result.

If you repeat a value later, do it under the same conditions. Same laboratory, same time of day, same situation. Otherwise you are comparing two figures that do not belong together. And after a lifestyle change, do not expect a difference within two weeks; SHBG moves over months.