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Free Androgen Index (FAI) Blood Test

Name: Free Androgen Index (FAI) Blood Test
Brand: Bloody Good
Price: 58.0 AUD
Availability: InStock

$58.00 AUD

Dealing with unwanted hair growth, acne, or irregular cycles and wondering whether excess androgen activity could be the cause?

Calculates the ratio of total testosterone to SHBG to estimate biologically active androgen levels. Used to investigate PCOS, hirsutism, acne, and irregular periods where androgen excess is suspected but total testosterone appears normal.

You will be emailed a referral to take to your local collection centre. If you ever have any questions, we're here to help.

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How It Works

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Order a test

Order the private test that suits you and your goals. After ordering, you will receive your referral by email.

Collect the sample

Attend one of our 4000+ partner collection centres throughout Australia. Search locations.

Receive your results

View all your lab results in your secure health dashboard. Easy!

Overview

The free androgen index (FAI) is a calculated ratio that estimates how much testosterone in your blood is biologically active. It is worked out by dividing total testosterone by sex hormone binding globulin (SHBG) and multiplying by 100. The result gives your practitioner a practical measure of androgen activity that accounts for how much testosterone is bound (and therefore inactive) versus free to act on tissues.

Most testosterone in the blood is bound to SHBG and albumin. Only a small fraction circulates unbound, and this free portion is what exerts biological effects. SHBG levels vary significantly between individuals and are influenced by insulin resistance, obesity, thyroid function, liver health, and oestrogen-containing medications. When SHBG is low, more testosterone is free and active even if the total testosterone reading looks normal. This is why the FAI is a more useful marker of androgen activity than total testosterone alone, particularly in women.

The FAI is primarily used in the investigation of androgen excess in women. A high FAI supports the biochemical evidence of elevated free androgens, which is one component of the criteria used to assess polycystic ovary syndrome (PCOS). Women with hirsutism (excess body or facial hair), persistent acne, scalp hair thinning, or irregular periods where androgen excess is suspected may have a normal total testosterone but an elevated FAI that explains their symptoms.

The FAI is most informative when reviewed alongside other hormonal markers including LH, FSH, oestradiol, prolactin, and DHEAS. An elevated FAI on its own does not confirm a diagnosis. Your GP, gynaecologist, or endocrinologist will use it as one piece of a broader hormonal and clinical assessment before drawing conclusions or recommending treatment.

Symptoms

Essential for women with suspected PCOS, androgen excess symptoms (acne, hirsutism), low libido, or anyone needing accurate bioavailable testosterone assessment.

Questions

The free androgen index (FAI) is calculated by dividing total testosterone by sex hormone binding globulin (SHBG) and multiplying by 100. It estimates the proportion of testosterone that is biologically available (free), rather than bound and inactive. A high FAI suggests more free androgen is circulating, which can explain symptoms of androgen excess even when total testosterone is within the normal range.
Free testosterone can be measured directly using specialised methods (such as equilibrium dialysis) or estimated from total testosterone and SHBG. The FAI is a calculated ratio that also uses total testosterone and SHBG, and it is widely used in clinical practice for assessing androgen excess in women because it is simpler and correlates well with symptoms. Direct free testosterone measurement is generally preferred for men where precision at lower androgen ranges matters more.
SHBG is a carrier protein that binds tightly to testosterone and makes it biologically inactive. When SHBG is low (which can occur with insulin resistance, obesity, hypothyroidism, or certain medications) more testosterone is free to act on tissues. This is why someone with a normal total testosterone but low SHBG can still experience symptoms of androgen excess. The FAI captures this dynamic in a single ratio.
The FAI is one of several markers assessed in a PCOS hormonal workup, but it is not the sole basis for a diagnosis. PCOS is diagnosed using a combination of clinical criteria (menstrual irregularity, signs of androgen excess, ovarian appearance on ultrasound) and hormonal markers. An elevated FAI supports the androgen excess component of the assessment but does not confirm PCOS on its own.
Yes. Many combined oral contraceptive pills raise SHBG, which will lower the FAI. If you stop the pill before testing, SHBG takes several weeks to return to baseline. Let your practitioner know what contraception you use so the result can be interpreted with this in mind.
No fasting is required for a free androgen index test. You can eat and drink normally before collection.

Dr. Vu Tran
Bloody Good’s Chief Medical Officer

How to prepare

No fasting is required. Eat and drink normally beforehand.

No specific cycle timing is required for FAI, though your practitioner may request testing alongside other early-cycle hormones (LH, FSH, oestradiol) for a complete picture. Let your practitioner know if you are taking hormonal contraceptives or androgen-blocking medications, as these will affect your SHBG and testosterone levels.

After the test

Share your results with your GP, gynaecologist, or endocrinologist. An elevated FAI alone does not constitute a diagnosis. It is one input into a broader hormonal assessment. Your practitioner will consider the FAI alongside other markers and your clinical presentation before drawing any conclusions or recommending further investigation.

Your test results will be available in your private dashboard. If there are any urgent issues, we'll let you know so you can follow up with your health professional.

Understanding results

The FAI is reported as a unitless ratio (testosterone in nmol/L divided by SHBG in nmol/L, multiplied by 100). Reference ranges vary by sex. In women, a high FAI generally indicates elevated free androgen activity and is one marker used in the assessment of PCOS and androgen excess.

Because the FAI is a ratio rather than a direct measurement, it captures situations where SHBG is suppressed (for example by insulin resistance, obesity, or certain medications) causing more testosterone to be biologically active even if total testosterone appears normal.

Your practitioner will interpret the FAI alongside LH, FSH, prolactin, DHEAS, and clinical symptoms to build a complete hormonal picture.

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Frequently Asked Questions

Do I need to book ahead?

Most collection centres accept walk-ins. Some may require a booking - check details when you click on your chosen location.

How do I know if I need to fast?

If your test needs fasting, we’ll include that in your instructions after you order. Fasting usually means no food for 8–12 hours, but water is fine.

What do I need to bring?

Just your pathology referral form (we email it to you)

Can I bring someone with me?

Of course. Just maybe don’t bring the friend who faints at the sight of blood.

What’s a phlebotomist?

They’re the highly trained professionals who take your blood sample - with a steady hand and a sharp needle. They love blood, but don’t worry… they’re not vampires. Just legends who make blood tests quick, clean, and (almost) painless.

What other samples may I need to provide for my test?

Some of our tests include Urine, Stool, Saliva and more. Each test will have a clear description on what sample you will need to give and instructions on how.