Free testosterone: normal range and how it is calculated

Free testosterone is the share of testosterone in the blood that is not bound to a protein, and so is available to the body's tissues. Often it is not measured directly but calculated from total testosterone and SHBG, usually with albumin as well, which is also how Clare's panel handles it. It matters most when total testosterone is borderline or SHBG is unusual.

What it measures

Most testosterone in the blood is bound to proteins, chiefly sex hormone-binding globulin (SHBG) and albumin, and a small share circulates free. Hormone held by SHBG cannot act on tissues. A total testosterone result counts all of it, so it can mislead when SHBG is high or low: a man with high SHBG can have a total within range and still have little free testosterone, and symptoms can follow the free figure rather than the total.

How it is worked out

The reference approach, equilibrium dialysis, separates free hormone from bound in the laboratory, but it is slow and not suited to routine testing. In 1999, Vermeulen and colleagues compared the simpler alternatives. Free testosterone calculated from total testosterone and SHBG matched equilibrium dialysis almost exactly in every condition studied except pregnancy. Direct "analogue" immunoassays for free testosterone gave values that were a fraction of the true figure, and the free androgen index drifted with SHBG, so neither was a reliable stand-in.

The Endocrine Society recommends a free testosterone result, by equilibrium dialysis or an accurate formula, for men whose total is near the lower limit or who have a condition that alters SHBG. The 2023 international PCOS guideline says free testosterone should be assessed by calculation, equilibrium dialysis or ammonium sulfate precipitation, and that direct immunoassays have limited accuracy.

How Clare's panel handles it

In Clare's panel, calculated free testosterone is a derived biomarker. The lab measures total testosterone, SHBG and albumin, and Clare solves the Vermeulen equation. In words: it uses fixed binding strengths for SHBG and for albumin, then works out how the measured total testosterone divides between SHBG, albumin and the free state. The answer is reported in pmol/L. Clare also calculates the free androgen index, a simpler figure used mainly for women:

Free androgen index = 100 × total testosterone ÷ SHBG (both in nmol/L)

Normal range

Free testosterone is reported in pmol/L or nmol/L by many laboratories and in pg/mL by others (1 pg/mL is about 3.47 pmol/L). Because the result depends on the formula and on the assays behind it, ranges vary more than for most markers.

Ranges vary by laboratory, method, age and sex, and the range on your own report is the one to read against. Two research figures help place a man's result. In 456 healthy non-obese men aged 19 to 40 in the Framingham Heart Study, the lowest 2.5% of calculated free testosterone sat below 70 pg/mL, about 243 pmol/L. In the European Male Ageing Study, sexual symptoms became more likely as free testosterone fell through 160 to 280 pmol/L, and late-onset hypogonadism was defined as three sexual symptoms with free testosterone below 220 pmol/L and total testosterone below 11 nmol/L. In women, both total and free testosterone fall with age.

What a low or high result usually points to

In men, a low free testosterone with symptoms is handled like a low total: confirmed on a repeat morning fasting sample, then followed by LH and FSH to tell a testicular cause from one in the pituitary gland or hypothalamus. A low free figure with a total in range usually comes with a high SHBG, from ageing, an overactive thyroid, liver disease or oestrogen-containing medicines.

In women, a higher free testosterone is one way doctors confirm biochemical androgen excess when polycystic ovary syndrome (PCOS) or another androgen condition is being considered. In men, a high figure can follow testosterone or anabolic steroid use.

What moves it

Anything that moves total testosterone or SHBG moves the calculated figure: time of day, food, age, weight, thyroid function and hormone medicines. In the Massachusetts Male Aging Study, free testosterone was about 2% lower for each year of age, a steeper fall than total testosterone. The formula also assumes normal binding: in pregnancy, estradiol takes up part of SHBG's binding sites and the calculated value runs below the true one. High-dose biotin can disturb some of the immunoassays used for total testosterone.

Preparing for the test

Because the figure is built on total testosterone, prepare as for that: a morning sample, between about 7 and 11 am, fasting, when you are well. Testosterone was 20 to 25% lower at 4 pm than at 8 am in men in their thirties, and fell by about 25% after a sugary drink. Mention hormone medicines, steroids and supplements such as biotin to the person taking the sample, and do not stop anything without your doctor's advice.

Price

When we read public prices on 11 October 2026, a free testosterone test on its own cost 90 at each of the 2 UAE providers that listed one. Those listings do not say whether free testosterone is measured directly or calculated. VAT was not stated at one, and the other adds a home collection fee of 100 on orders under 300 without a package. Free testosterone is also sold inside testosterone and male hormone packages.

Related tests

Free testosterone is built from total testosterone, SHBG and albumin, so it is read next to them; the testosterone test brings these together. LH and FSH help explain where a low result starts. Our article on what to expect from a comprehensive blood test in Dubai shows where hormone markers sit in a full panel.

Why the number means more over time

Free testosterone is most useful as a trend measured the same way: same laboratory, same formula, morning fasting samples. Guidelines ask for a repeat before a low result is acted on, and population studies show a gradual fall with age. A drop well beyond that, or a change that tracks weight, illness or a new medicine, is worth discussing with a doctor, with your results side by side. Clare is opening with a waitlist at clare.health.