SHBG and testosterone in men: what your result really says

SHBG is a protein that binds your sex hormones and transports them through the blood. On a men's hormone panel it appears as SHBG, short for sex hormone binding globulin. For a man reading his own results, that binding capacity is the brake on available testosterone.

It binds testosterone firmly and oestradiol far more loosely. Anything attached to SHBG cannot be used by your tissue. SHBG is not itself a sex hormone.

It is the transport protein that governs how available your hormones are.

The test measures how much of this protein circulates in your blood, reported in nmol/l. On its own that figure says little. It gains meaning beside your total testosterone.

Your free testosterone is then calculated from that pair. Part of your testosterone is loosely bound to albumin and stays usable. Only the fraction SHBG holds is effectively out of reach.

The reference values below are set per sex and per age group. In men that split is not cosmetic, because SHBG rises with age.

Picture a man of sixty whose SHBG comes back at 19 nmol/l. Against a flat male range of 18.3 to 54.1 that reads as normal. His own lower limit is 20.6, so he sits below it.

And a low SHBG in a man is exactly the finding that matters. The reverse happens as well. That same man at 70 nmol/l looks raised against the flat range.

His band runs up to 76.7, so he is simply normal. The gap between 54.1 and 76.7 is 42 per cent.

Reference values differ between laboratories and between analysers. We work with a network of independent, certified laboratories. They do not all run the same equipment. The range printed on your own report is therefore the one that counts.

You had your testosterone measured because the energy had gone. Your strength in the gym had stalled and your libido had dropped. The result came back normal.

And the symptoms stayed. This is the scenario in which SHBG is the missing number.

A total testosterone value is the sum of bound and free hormone. Change the amount of binding protein and that sum changes with it. With a high SHBG your total testosterone is propped up while the free fraction falls.

The result then looks reassuring and is not. With a low SHBG the opposite happens. The total drops while the free fraction holds steady.

You are then alarmed by a figure that means little in practice. Without SHBG beside it, both situations are read wrongly.

For men it does not end there. A low SHBG is a finding in its own right. The strongest driver is excess weight with insulin resistance.

A persistently high insulin level suppresses SHBG production in the liver. Type 2 diabetes, hypothyroidism, glucocorticoids and non-alcoholic fatty liver disease push the value down as well. What a low SHBG means in a man therefore depends mainly on his metabolism.

A normal total testosterone alongside such a value is not a clean bill of health.

There is one more cause, well known in strength sports and still often left out. Androgens and anabolic steroids strongly suppress SHBG production. The value can then fall far below the lower limit.

We do not recommend that use and we do not supervise it. But if you use it, or have used it, your doctor needs to know. Without that information your SHBG result simply cannot be interpreted.

Separately, SHBG is a metabolic signal in itself. Large prospective cohorts show the same thing. A low SHBG goes with a higher risk of type 2 diabetes.

That holds in both sexes. Mendelian randomisation points the same way. That is an association across groups.

It is not a prediction about you personally, and it is certainly not a diagnosis. If you want this figure beside your testosterone, you can order a separate SHBG test.

SHBG should not be requested on its own. Order it alongside your total testosterone, for example with a testosterone test. Only then can the result be read.

Have blood drawn in the morning, preferably between seven and ten. Testosterone follows a clear daily rhythm and peaks early. SHBG itself varies far less across the day.

But because you assess the two together, testosterone sets the timing. Fast beforehand if glucose, insulin or a lipid profile is included.

Have it measured when your energy, strength, muscle mass or libido have declined. Also when an earlier testosterone result was normal and the symptoms persisted anyway. SHBG is further worth having with central weight gain, with known insulin resistance and with fatty liver. In those situations a total testosterone value without SHBG is close to uninterpretable.

Do not measure during acute illness or straight after a heavy training block. Repeat an abnormal result before drawing conclusions from it. Compare your value against the correct age band rather than a flat male range. If your doctor suspects a broader androgen problem, DHT can be measured too.