Free Androgen Index Test | London Blood Tests UK

Assess androgen balance with our Free Androgen Index blood test from £48. UKAS-accredited results, fast turnaround, optional GP consultation.

The Free Androgen Index (FAI) Blood Test estimates the amount of biologically active testosterone in your body by calculating the ratio between total testosterone and sex hormone-binding globulin (SHBG). Available for £48, analysed in a UKAS-accredited laboratory, with results typically ready within 2–3 business days and an optional GP consultation for interpretation.

What is a Free Androgen Index (FAI) Test?

The Free Androgen Index (FAI) is a calculated value used to estimate free (active) testosterone — the fraction of testosterone that is not bound to proteins and is available to act on tissues.

Most testosterone in the bloodstream is bound to SHBG or albumin. When SHBG levels are high, less testosterone is biologically active; when SHBG is low, free testosterone increases. The FAI accounts for this interaction by using the formula:

FAI = (Total Testosterone ÷ SHBG) × 100

The FAI test is particularly valuable in women, where direct free testosterone assays are often unreliable. It is widely used to assess androgen excess, investigate polycystic ovary syndrome (PCOS), and evaluate symptoms such as hirsutism, acne, and menstrual irregularities. In men, it can help assess androgen availability when SHBG levels are abnormal.

Benefits of the Free Androgen Index Test

1. Accurate Estimate of Active Testosterone
   Provides a more clinically meaningful measure of androgen activity than total testosterone alone, especially when SHBG is abnormal.

2. Key Test for PCOS Investigation
   Elevated FAI is a common biochemical finding in women with PCOS and supports diagnosis when combined with symptoms and ultrasound findings.

3. Explains Androgen-Related Symptoms
   Helps identify hormonal causes of acne, excess facial/body hair, scalp hair thinning, and oily skin.

4. Useful in Menstrual & Fertility Assessments
   Androgen imbalance can disrupt ovulation and menstrual cycles; FAI helps clarify the hormonal picture.

5. Supports Male Hormone Evaluation
   In men with normal total testosterone but low SHBG, FAI can reveal excess free testosterone; conversely, high SHBG may mask deficiency.

6. Guides Treatment & Monitoring
   Useful for monitoring response to hormonal treatments such as combined oral contraceptives, anti-androgens, or testosterone therapy.

7. Optional GP Consultation for Contextual Review
   Results can be reviewed with a GP to interpret androgen status in relation to symptoms, cycle phase, and other hormone tests.

Why Do I Need a Free Androgen Index Test?

You may benefit from an FAI test if you experience symptoms or clinical concerns such as:

• Excess facial or body hair (hirsutism)

• Persistent acne or oily skin

• Scalp hair thinning or androgenic alopecia

• Irregular or absent menstrual cycles

• Difficulty conceiving

• Suspected or diagnosed PCOS

• Low libido or hormonal imbalance symptoms

• Abnormal SHBG levels affecting testosterone interpretation

FAI testing is most informative when interpreted alongside total testosterone, SHBG, LH, FSH, and oestradiol.

How the Test Works

In-Clinic Blood Test

1. Book Your Appointment

   • Book online or by phone; no referral required.

   • Women may be advised to test during the early follicular phase (day 2–5) of the menstrual cycle.

2. Pre-Test Preparation

   • No fasting required.

   • Inform the clinician about hormonal contraception, HRT, or androgen-affecting medications.

3. Blood Sample Collection

   • A qualified phlebotomist collects a venous blood sample.

   • The procedure takes around 5–10 minutes.

4. Sample Handling

   • Blood samples for testosterone and SHBG are labelled and transported to a UKAS-accredited laboratory.

5. Laboratory Analysis

   • Total testosterone and SHBG are measured using high-sensitivity immunoassays.

6. FAI Calculation

   • The laboratory calculates the Free Androgen Index using the validated formula.

7. Results Delivery

   • Results are typically available within 2–3 business days via your secure online portal.

8. Optional GP Consultation

   • A GP can interpret your results in relation to symptoms, fertility, or endocrine health.

At-Home Blood Draw (Home or Hotel Service)

1. Book a Home Visit

   • Choose a convenient time and location anywhere in the UK.

2. Professional Phlebotomist Visit

   • A certified phlebotomist attends your home or hotel with sterile equipment.

3. Blood Collection

   • A venous blood sample is taken just as it would be in clinic.

4. Secure Transport

   • Samples are couriered the same day to the laboratory.

5. Analysis & Reporting

   • Testosterone, SHBG, and FAI are analysed and calculated.

6. Results & Follow-Up

   • Receive results within 2–3 business days, with optional GP review available.

Your Free Androgen Index Results – Explained

FAI is reported as a unitless numerical value. Reference ranges vary by sex.

Typical UK Reference Ranges

Women

• Normal: 0.5–6.5

• Borderline high: 6.5–8

• High: > 8 (suggestive of androgen excess)

Men

• Normal: 30–150

• Interpretation in men depends strongly on SHBG and clinical context.

Interpretation

• High FAI
  Suggests androgen excess, commonly seen in PCOS, insulin resistance, or low SHBG states.

• Low FAI
  May indicate reduced androgen availability, high SHBG, or pituitary/gonadal dysfunction.

• Normal FAI
  Suggests balanced androgen activity, though symptoms may still warrant further investigation.

FAI should always be interpreted alongside total testosterone, SHBG, and clinical findings.