The panel / Androgens

SHBG

SHBG is the least discussed result on most men's panels and one of the most consequential. It is the protein that decides how much of your testosterone is locked away. Without it, a total testosterone number cannot be interpreted safely, because the same total can mean two opposite things.

What it measures

Sex hormone binding globulin is a carrier protein made by the liver. It binds testosterone tightly, and what it binds, your tissue cannot use. Around 40 percent of circulating testosterone is held by SHBG at any moment. Measuring it tells us how much of your total is genuinely available, and lets free testosterone be calculated properly.

What SHBG does

Carrier proteinBinds roughly 40 percent of circulating testosterone

Effect on the totalDetermines how much of a total result is actually usable

Needed for the calculationRequired, with albumin, to calculate free testosterone

SHBG is the reason two men with an identical total testosterone can have completely different amounts of usable hormone, and completely different symptoms.

SHBG does not swing through the day the way testosterone does, so its timing requirements are inherited from the testosterone draw it accompanies rather than being its own. There is no universally agreed SHBG standard across laboratory platforms, which is one reason repeat monitoring should stay with one laboratory.

Why it is on the panel

Because it is the one result that tells us whether the total testosterone can be taken at face value. If SHBG is normal, the total is a fair reflection of your androgen status and free testosterone adds nothing. If SHBG is abnormal in either direction, the total is misleading and the free fraction becomes the number that decides. Drawing testosterone without SHBG is how men get diagnosed wrongly in both directions.

How it is measured

SpecimenSerum, drawn with total testosterone

TimingMorning, with the testosterone draw

FastingYes, alongside testosterone

AssayStandardised immunoassay

Also neededAlbumin, to calculate free testosterone

TurnaroundTypically 2 to 4 days

Interpretation

Reading the result

Reference ranges are assay-specific and rise substantially with age, so the printed range on your report governs. As an illustration of how much age matters, one reference study found a range of roughly 13 to 57 nmol/L at age 30 and roughly 28 to 101 nmol/L at age 70.

Bands used in practice

Low SHBGTotal testosterone reads lower than your usable hormone. Look to weight, insulin resistance, or an overactive thyroid.

Normal SHBGThe total can be taken at face value, and free testosterone confirms rather than changes it.

High SHBGTotal testosterone reads higher than your usable hormone. A normal total here can hide genuine deficiency.

An abnormal SHBG is not itself a disease. It is a signal that the total testosterone needs reinterpreting, and usually a pointer to something else worth finding.

What raises and lowers it

These are the common drivers. Several are treatable, and treating them changes the testosterone picture without any hormone being prescribed.

9 things that move it

Raised by ageing, which is the most common reason in men over 50

Raised by an overactive thyroid

Raised by liver disease, and by oestrogen exposure

Raised by anticonvulsants including carbamazepine, phenytoin and phenobarbital

Raised by sustained heavy alcohol intake, and by severe under-eating

Lowered by obesity, insulin resistance and type 2 diabetes, the most common reason in younger men

Lowered by an underactive thyroid, and by growth hormone excess

Lowered by glucocorticoids, by progestins, and by exogenous testosterone or anabolic steroids

Lowered by nephrotic syndrome and by advanced cirrhosis

What happens next

If SHBG is abnormal, free testosterone is calculated or measured, because the total can no longer be interpreted alone.

If SHBG is low and free testosterone is normal, the total is a red herring. Weight, glucose and sleep are addressed rather than hormones.

If SHBG is high and free testosterone is low despite a normal total, that is genuine deficiency, and LH and FSH follow to find the cause.

An unexplained SHBG result prompts a look at thyroid function, liver function and the medication list, because it is often the first sign of one of those.

Straight answers

Often, yes, by treating whatever is moving it. Losing excess weight and improving insulin sensitivity raises a suppressed SHBG. Treating thyroid disease moves it back in whichever direction the thyroid was driving it. Cutting sustained heavy drinking lowers a raised one. It is rarely a target in itself, but it usually improves as a by-product of fixing the real problem.