Free testosterone, total testosterone and SHBG: the difference

What is total testosterone?

Total testosterone is the value most people recognise from their reports. It measures all the testosterone in the blood, both the portion bound to proteins and the small portion moving freely. As an overview value it works well, and it is the total value that Swedish reference intervals and clinical guidelines are built on.

At the same time, the total says nothing about how the hormone is distributed. Two men with exactly the same total value can have different amounts of usable testosterone, depending on how much of it sits attached to carrier proteins. That is where the other two values come in.

What is free (bioactive) testosterone?

Free (bioactive) testosterone is the part of the hormone that is not attached to any carrier protein and can therefore be taken up by muscle, brain, bone and other tissues. According to a review in the journal Endocrine Reviews, this is only about 1 to 4 percent of all the testosterone in the blood.

That sounds small, but it is the share that does the work. When symptoms like tiredness, reduced desire or slower recovery need explaining, it is in practice the free portion that matters, since bound hormone is inactive in the moment.

What does SHBG do?

SHBG, sex hormone binding globulin, is a protein made in the liver that binds sex hormones tightly. Most bound testosterone sits either on SHBG or, more loosely, on albumin (a common carrier protein in the blood).

The SHBG level therefore decides how large a share of the total is free. SHBG normally rises with age, one reason free testosterone falls faster than the total in older men. Excess weight tends to pull SHBG down instead, and the thyroid, the liver and certain medicines can shift the level in either direction. SHBG is not a hormone itself, but rather the dial that sets how much of the hormone is available.

Why can the total value mislead?

Because SHBG varies from person to person, the same total value can mean different things. Some typical patterns, simplified:

| Total testosterone | SHBG | Free share | What it can mean | | --- | --- | --- | --- | | Normal | High | Low | A deficiency can hide behind a normal total value | | Low | Low | Normal | Often no true deficiency | | Low | Normal or high | Low | Points more toward true deficiency, investigated further |

Swedish clinical guidance makes exactly this point: a low total value alongside a low SHBG need not mean testosterone deficiency, which is why low values are always followed up with SHBG. The table is a simplification and never replaces a doctor's assessment, but it shows why the three values belong together.

How do you test free testosterone and SHBG?

All three values are measured in one and the same blood draw, no referral needed. You walk in to a sampling location when it suits you, preferably fasting in the morning since testosterone varies over the day.

Male Hormone Test Base is built around exactly this question. The test measures total testosterone, free (bioactive) testosterone, SHBG with ratio and albumin, the whole chain from total level to available hormone. With every value in the same report, you can see whether an off total value comes down to hormone production or to the carrier proteins.

When should you see a doctor?

See a doctor if you have complaints that suggest hormone deficiency, for example reduced desire, erectile problems, long-standing tiredness or shrinking muscle mass, especially combined with low measured values. Swedish clinical guidance requires symptoms and at least two low morning values before testosterone deficiency is even considered, and the workup involves more values than those described here.

This article explains what the values mean, but interpreting your particular numbers, in your particular context, is always a job for a doctor.

Male Hormone Test Base measures total and free testosterone, SHBG with ratio and albumin in a single draw, no referral needed.

This article is general health information, not medical advice and not an assessment of your values. If you have symptoms or concerns, contact your healthcare provider.