The free androgen index (FAI) test is a simple calculation that compares your total testosterone with SHBG, the protein that binds it. It gives a quick estimate of how much testosterone is free to act, and it is used mainly in women, especially when checking for polycystic ovary syndrome (PCOS).
Your FAI can help explain acne, excess hair growth or irregular cycles. We read it with your testosterone, SHBG, insulin and cycle timing, against optimal ranges, so a ratio doesn't get read out of context.
FAI is included in Vively's Female Hormone Health Test, Perimenopause and Menopause Hormone Tests, and for men, the Male Hormone Health Test. You start with your Baseline Health Check, then add the hormone test that fits you.
Every marker in range? Get your $99 back. T&Cs apply.Want to save 25%? Try our 4-Month Reset insteadThe free androgen index (FAI) is a calculated ratio, shown as a percentage, that estimates how much of your testosterone is free to act on your tissues. It compares total testosterone with SHBG, the protein that binds it, and is most reliable in women.
The lab works it out from two results in nmol/L: FAI = (total testosterone ÷ SHBG) × 100.
Sex hormone-binding globulin (SHBG) is a protein made by your liver that holds testosterone tightly. When SHBG is high, less testosterone is available. When it is low, more is.
For example, a woman with a total testosterone of 1.5 nmol/L and SHBG of 50 nmol/L has an FAI of 3%. If her SHBG falls to 15 nmol/L, which can happen with insulin resistance, her FAI rises to 10%, even though her testosterone hasn't changed.
FAI shows whether a woman has more active androgen than expected, which total testosterone alone can miss. Many women with PCOS have a normal total testosterone, and the clue is a low SHBG, driven by insulin resistance, pushing FAI up.
That is why the international PCOS guideline recommends FAI, free testosterone or bioavailable testosterone over total testosterone alone for checking high androgens in the blood (biochemical hyperandrogenism).
Because it is calculated, FAI is less reliable in men, when SHBG is very low, as small changes then swing FAI widely and can overstate free testosterone, and in pregnancy, when SHBG rises sharply.
Normal does not always mean optimal. An FAI near the top of the female range, with rising fasting insulin, is an early signal worth acting on even before periods or skin change.
For adult women, a typical FAI is about 0.7 to 8.6%. Men's FAI is much higher, about 14.5 to 80.3%, but it is a poor guide in men.
| Range | |
|---|---|
| Typical lab reference range (adult women) | 0.7 to 8.6% |
| Vively optimal range (women) | Under 5% |
| Typical lab reference range (adult men) | 14.5 to 80.3% |
| Vively optimal range (men) | Not used. We look at free testosterone instead |
FAI ranges differ between labs because testosterone and SHBG assays differ, so check the range on your report. Optimal ranges are what we aim for to support long-term health, not diagnostic cut-offs. An FAI above 5% is a prompt to look at your insulin, cycles and symptoms. It does not diagnose PCOS on its own.
In women, a high FAI most often points to polycystic ovary syndrome (PCOS), usually alongside low SHBG and insulin resistance. It can also come from supplements or, less commonly, an adrenal condition.
Common reasons:
Less common causes include non-classic congenital adrenal hyperplasia and, rarely, an androgen-producing tumour.
A low FAI in women usually means SHBG is high, most often because of the combined pill or oral oestrogen. It is rarely a medical problem by itself.
In men, FAI swings with SHBG, so a high or low reading means little on its own. Free testosterone, from early-morning samples, is the result to act on.
Anything that shifts testosterone or SHBG will shift your FAI, and SHBG is the more changeable of the two.
Do you need to fast? Not for FAI itself. If you test alongside your Baseline, you'll fast overnight anyway, which lets us read glucose and insulin next to your FAI.
FAI is most useful read with the markers that explain why it is high or low.
| Pattern | What it can mean |
|---|---|
| High FAI, normal total testosterone, low SHBG, high fasting insulin or HOMA-IR | Insulin resistance is likely lowering SHBG. A common PCOS pattern. |
| High FAI and high total testosterone with irregular periods | Fits with PCOS. Needs GP review to confirm and rule out other causes. |
| High FAI with high DHEA-S | Androgens may be coming partly from the adrenal glands. Needs GP review. |
| Low FAI with high SHBG while on the combined pill | The expected effect of the pill. Not a concern by itself. |
For a high FAI, the lifestyle changes that work best are the ones that improve insulin resistance, because they lift SHBG and lower free androgens. They help many women with PCOS but won't change an adrenal condition or a tumour.
See your GP if your FAI is above your lab's range together with irregular or absent periods, acne or excess hair growth, or trouble getting pregnant. These can point to PCOS, which is worth diagnosing properly because it affects long-term heart and diabetes risk.
See your GP promptly if androgen symptoms appear quickly over a few months, if your voice deepens, or if your total testosterone is very high.
FAI is included in our Female Hormone Health Test, Perimenopause Hormone Test, Menopause Hormone Test, Weight Management Test and Full Body Health Check, and for men, the Male Hormone Health Test. You start with your Baseline Health Check, and the exact markers can depend on the referring doctor's review.
We arrange your referral through our GP network, and you have one blood draw at one of 3,700+ accredited partner collection centres. Results arrive in the app, usually within a few days, against optimal ranges. Your practitioner explains what's driving your FAI, builds a personalised plan, and you retest to track change.
Order the Female Hormone Health Test, or the Male Hormone Health Test for men.
No, FAI doesn't need fasting. If you're testing with Vively's Baseline, you'll fast overnight anyway because it includes fasting glucose and insulin, which help explain a high FAI. If you have periods, book your test for day 2 to 5 of your cycle.
For a woman, yes. It is above the typical female range of 0.7 to 8.6% and is often linked to PCOS or low SHBG from insulin resistance. Look at your periods, symptoms, SHBG and fasting insulin, and see your GP to confirm the cause. For a man, 10% is below range, but FAI is a poor guide in men.
FAI is a quick ratio of total testosterone to SHBG. Free testosterone is calculated with a fuller formula that also uses albumin and is reported in pmol/L. In women, they usually agree. In men, and when SHBG is very low, free testosterone is the more reliable of the two.
Yes, but the result will reflect the pill. The combined pill raises SHBG, which lowers FAI and can hide high androgens. If you're being checked for PCOS, talk with your GP about timing. For general tracking, we note that you're on the pill when reading your result.
Not very. Men have much more testosterone relative to SHBG, so the simple ratio doesn't reflect how much testosterone tissues receive. Free testosterone, ideally from two early-morning samples on different days, is the better marker for men and is included in our Male Hormone Health Test.
Many blood tests can be Medicare-funded when a doctor orders them for a clinical reason. With Vively, we arrange the referral through our GP network, so you don't need a separate GP appointment before your hormone test. Your own GP can also order testosterone and SHBG, which FAI is calculated from, when there is a clinical reason.
Among 1,878 Vively members tested in 2024 to 2026, women aged 40 to 49 had a median FAI of 1.0% (middle half 0.8 to 1.6). Men the same age: 50.0%. The lab range is 0.7 to 8.6% for women and 14.5 to 80.3% for men. A member median is not a target.
The line is the median member at each age. The shaded bands show where most members sit. The dashed red lines are the lab range.
| Group (%) | Members | Median | Middle 50% | 5th to 95th percentile | Lab range |
|---|---|---|---|---|---|
| Women 18 to 29 | 68 | 1.8 | 1.0 to 2.6 | 0.6 to 5.2 | 0.7 to 8.6 |
| Women 30 to 39 | 304 | 1.3 | 1.0 to 2.0 | 0.5 to 4.1 | 0.7 to 8.6 |
| Women 40 to 49 | 393 | 1.0 | 0.8 to 1.6 | 0.4 to 3.3 | 0.7 to 8.6 |
| Women 50 to 59 | 281 | 1.2 | 0.9 to 2.0 | 0.4 to 3.8 | 0.7 to 8.6 |
| Women 60 and over | 123 | 1.1 | 0.8 to 1.9 | 0.4 to 3.3 | 0.7 to 8.6 |
| Men 18 to 29 | 75 | 60.6 | 47.4 to 74.7 | 21.9 to 168.4 | 14.5 to 80.3 |
| Men 30 to 39 | 204 | 53.1 | 42.0 to 64.8 | 33.4 to 96.0 | 14.5 to 80.3 |
| Men 40 to 49 | 243 | 50.0 | 41.0 to 59.0 | 33.0 to 97.6 | 14.5 to 80.3 |
| Men 50 to 59 | 125 | 42.5 | 37.3 to 52.0 | 26.0 to 72.0 | 14.5 to 80.3 |
| Men 60 and over | 62 | 37.3 | 31.1 to 45.1 | 25.2 to 64.3 | 14.5 to 80.3 |
Pick your sex and age, then type your result.
What is a normal FAI for my age?
Among 1,878 Vively members (first blood test, January 2024 to October 2026), the median FAI for women was 1.8% at 18 to 29, 1.3 at 30 to 39, 1.0 at 40 to 49, 1.2 at 50 to 59 and 1.1 at 60 and over. For men it was 60.6% at 18 to 29, 53.1 at 30 to 39, 50.0 at 40 to 49, 42.5 at 50 to 59 and 37.3 at 60 and over.
The lab range is 0.7 to 8.6% for women and 14.5 to 80.3% for men. A member median is not a target or a diagnosis. If your result is outside the range on your report, talk to your GP.
How to get it: Available as one of our specialty add-on tests. Your test referral is issued straight away when you order. See how a blood test without a referral works.
Related tests: Free testosterone, FSH, DHEA, Dehydroepiandrosterone Sulfate (DHEA-S)
Guide: Testosterone levels in women by age, including the free androgen index by age.
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