What is free testosterone?
Of all the testosterone in your blood, most is attached to protein: tightly to SHBG and loosely to albumin. Only the part circulating free, a few percent, can enter the cell and do its work in muscle, bone, brain and skin. Free testosterone is that part. It is not measured separately; a direct measurement exists but is laborious and rarely needed. Instead it is calculated with a formula from three values you already have: total testosterone, SHBG and albumin, based on how strongly testosterone binds to each of those two proteins. The outcome is an estimate, and a good one, as long as the input is right. Your report shows free testosterone in pmol/L, so in a unit a thousand times smaller than the total. Normal is 210 to 619 pmol/L in a man of 20 to 50 years and 3 to 26 pmol/L in a woman of the same age, where the labs overlap; the range falls with age, and like the total it applies to a morning value.
Why is free testosterone relevant?
Total testosterone is usually enough. Free testosterone becomes interesting as soon as SHBG is abnormal, and that is more often than you think. In a man with belly fat SHBG is low, so a low total testosterone still yields a reasonable free part; in an older man or a man with an overactive thyroid SHBG is high, so a normal total still leaves too little free. In both cases free testosterone fits how someone feels better than the total does. In women free testosterone is the better androgen number. In PCOS SHBG is low from insulin resistance, and then free testosterone is raised while the total still looks normal; excess hair growth, acne and an irregular cycle go with that free part. On the pill the opposite happens: SHBG rises strongly and free testosterone falls, which often does the skin good and desire sometimes not. For anyone who wants to stay healthy the gain sits in the combination. Losing weight around the middle raises both the total and SHBG in a man, and so distributes the free part more healthily; in a woman with PCOS the same change lowers free testosterone through a rising SHBG. The free number is therefore the value in which you see the lifestyle change back most honestly.
Free testosterone reference ranges
What counts beside the number:
- Total testosterone and SHBG, the input: they show which of the two is steering the free part
- The time: the total is drawn in the morning, so the range applies to a morning value
- Your waist, sleep, alcohol, training load and stress, the levers of the total
- The pill, an overactive or underactive thyroid and eating too little, the levers of SHBG
- In women: cycle, excess hair growth and acne, which point at PCOS
- The lab: the formula and the range differ per lab, so follow it at the same one
The bands above are where the labs overlap; the range on your own report may be wider, and there is no national normal value. Free testosterone is calculated, not measured, and the formula and the range differ per lab; so follow the value at the same lab. One lab lists the free androgen index, a percentage, under the name free testosterone, and that has a page of its own.
What Dutch labs actually use
Three labs publish a reference value for calculated free testosterone. Clinical Diagnostics is missing here, and that is not an omission: its page with almost the same name is about the free androgen index, a percentage rather than a concentration, and that index has a page of its own. For men under fifty the three sit furthest apart. Unilabs holds 210 to 813 pmol/L, Star-shl 198 to 619 pmol/L and Certe 165 to 655 pmol/L. For women Unilabs publishes 1 to 41 pmol/L, Star-shl 3 to 33 pmol/L and Certe 2.3 to 26 pmol/L. Star-shl states beside its table where the number comes from: Vermeulen et al., 1999, next to the manufacturer's package insert. Free testosterone is not measured but calculated, from your total testosterone, your SHBG and your albumin.
3 – 26pmol/L
Between 1 and 3 and between 26 and 41 it depends on the lab, because each sets its limits on its own method and population. Above 41 every lab calls it abnormal.
every lab calls 3 – 26 pmol/L normal. Between 1 and 3 and between 26 and 41 it depends on the lab.
Every age, per lab
| Laboratory | Group | Reference range |
|---|---|---|
| Unilabs(Saltro, Medlon, SHO, Atalmedial)2026 | Men 20 to 50 yrs | 210–813 pmol/L |
| Men 50 to 80 yrs | 185–750 pmol/L | |
| Men from 80 yrs | 156–686 pmol/L | |
| Women 20 to 50 yrs | 1–41 pmol/L | |
| Women from 50 yrs | 1–27 pmol/L | |
| Star-shl2026 | Men 20 to 49 yrs | 198–619 pmol/L |
| Men from 50 yrs | 163–473 pmol/L | |
| Women 20 to 49 yrs | 3–33 pmol/L | |
| Women from 50 yrs | 1–20 pmol/L | |
| Certe2026 | Men from 18 yrs | 165–655 pmol/L |
| Women from 18 yrs | 2.3–26 pmol/L |
Each band as the lab publishes it, retrieved in 2026, unless marked otherwise.
Free testosterone high or low: what it means
A low free testosterone has two routes: a low total, or a high SHBG. The first route is the causes of a low testosterone itself: drawn too late, belly fat, lack of sleep, stress, alcohol, overtraining, age, and medicines such as opioids and prednisone. The second route is an SHBG rising from age, the pill, an overactive thyroid or eating too little. With the total and SHBG beside it, you see which of the two is steering the free part, and that decides the lever. A high free testosterone in men is usually testosterone from outside. In women it is usually PCOS: a normal or slightly raised total with a low SHBG, and insulin resistance underneath. A strongly raised value, a multiple of the range, is rare and calls for investigation of ovaries and adrenal glands. The levers are those of total testosterone and SHBG together: losing weight around the middle, strength training, seven to eight hours of sleep, less alcohol, less sugar and fast carbohydrates, and enough food for what you train. In men that lifts the total and normalises SHBG; in women with PCOS the same change lets SHBG rise and free testosterone fall. Count on three to six months. Never read free testosterone apart from the numbers it follows from. An abnormal albumin, in serious illness or malnutrition, carries through into the outcome. And when comparing over time, keep to one and the same lab, because the formula and the range differ per lab.
What lowers it
A low total, or a high SHBG; the numbers beside it show which of the two.
| Cause | How often |
|---|---|
| A low total testosteroneThe input the calculation starts from: drawn too late, belly fat, lack of sleep, stress, alcohol, overtraining, age or medicines that shut production down | Often |
| A high SHBGMore binding protein leaves less free at the same total; the pill, age, an overactive thyroid and eating too little raise SHBG | Often |
| An abnormal albuminIn serious illness or malnutrition albumin falls, and the formula carries that through; the outcome is then less reliable | Rare |
What raises it
A high total, or a low SHBG; in women the latter is the usual route.
| Cause | How often |
|---|---|
| A low SHBGLess binding protein leaves more free at the same total; belly fat, insulin resistance and in women PCOS are the most common causes | Often |
| A high total testosteroneIn men usually testosterone from outside, from a gel, injection or anabolic steroids; in women PCOS or rarely a tumour of the ovary or adrenal gland | Often |
How does a free testosterone blood test work?
- Referral
- Not needed. Free testosterone follows from total testosterone, SHBG and albumin; request those three together or have the lab supply the calculation.
- When to draw
- Before ten in the morning, after a normal night, preferably before breakfast, because the total this value follows from is then highest and cleanest.
- The draw
- One tube of blood from a vein in your arm; all three input values come from that same tube.
- The result
- A single number in pmol/L, with one range for men and one for women; note that it is a unit a thousand times smaller than the total. Usually available within a few days.
- Repeating
- A low value on a second morning, together with the total. After losing weight, strength training or sleeping better you see the difference after three to six months.
- Where to draw
- You can draw at 250+ locations near you, no referral needed. See the locations
Frequently asked questions
What is free testosterone?
The part of your testosterone not bound to SHBG or albumin and therefore able to enter the cell and do its work: a few percent of the total. It is not measured separately but calculated from three values you already have, total testosterone, SHBG and albumin. It says more than the total as soon as SHBG is abnormal.
What is a normal free testosterone level?
In a man of 20 to 50 years 210 to 619 pmol/L and from 50 years 185 to 473 pmol/L; in a woman of 20 to 50 years 3 to 26 pmol/L and from 50 years 2.3 to 20 pmol/L. Mind the unit: pmol/L is a thousand times smaller than the nmol/L of the total. The range on your own report may differ, because the formula differs per lab.
What does a low free testosterone mean?
That there is little active testosterone, and that can come by two routes: a low total, from the usual causes such as belly fat, lack of sleep, stress, alcohol, overtraining or age, or a high SHBG, from age, the pill, an overactive thyroid or eating too little. The two numbers beside it show which route it is, and that decides what you do about it.
What does a high free testosterone mean?
In men usually testosterone from outside. In women usually PCOS: the total is normal or slightly raised, but a low SHBG from insulin resistance lets too much androgen act, with excess hair growth, acne and an irregular cycle as the result. Losing weight and less sugar let SHBG rise and the free part fall.
When does free testosterone say more than the total?
As soon as SHBG is abnormal. In a man with belly fat SHBG is low and the free part is better than it looks at a low total; in an older man or with an overactive thyroid SHBG is high and the free part is worse than it looks at a normal total. In women with PCOS free testosterone is raised while the total looks normal. In all those cases the free number fits the complaints better.
How do I improve my free testosterone?
With the levers of the total and SHBG together: losing weight around the middle, strength training, seven to eight hours of sleep, less alcohol, less sugar and fast carbohydrates, and enough food for what you train. In men the total rises and SHBG normalises; in women with PCOS SHBG rises and free testosterone falls. Count on three to six months, and measure in the morning at the same lab.
Is free testosterone measured or calculated?
Calculated, with a formula from total testosterone, SHBG and albumin, based on how strongly testosterone binds to those two proteins. A direct measurement exists, but is laborious and rarely needed. Because the formula and the range differ per lab, the value can only be compared over time at the same lab.
Do I have to fast for this test?
Preferably yes, and above all early: the total this value follows from is highest before ten in the morning and temporarily lower after a meal. Have total testosterone, SHBG and albumin taken from the same tube.
Which tests include free testosterone?
Free testosterone is in the Hormones men test (€129, also as an add-on for €109).
Related biomarkers
Read on
Sources
- 1.Unilabs, test catalogue (Dutch): free testosterone. 2026. bepalingenklapper.nl
- 2.Star-shl, test catalogue (Dutch): free testosterone. 2026. star-shl.nl
- 3.Certe, test catalogue (Dutch): free testosterone (calculated). 2026. bepalingenwijzer.certe.nl
- 4.Vermeulen et al., A critical evaluation of simple methods for the estimation of free testosterone in serum, J Clin Endocrinol Metab. 1999. pubmed.ncbi.nlm.nih.gov
Educational information only, not medical advice. Consult a healthcare professional for clinical decisions.
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