1. Home
  2. Knowledge Base
  3. Medical
  4. Pathology
  5. SGBH, Free Androgen Index and Testosterone Levels in Hormone Therapy

SGBH, Free Androgen Index and Testosterone Levels in Hormone Therapy


In gender-affirming care, it’s not just about the total amount of testosterone in your body, but also how much of it is actively working to create masculine changes. The Free Androgen Index (FAI) helps us understand this better. It tells us about the testosterone that is free to act on your body, which is really important if you’re taking testosterone but not seeing the expected changes, like a deeper voice or more body hair. So, while keeping an eye on the overall testosterone level is good, checking the FAI can give us extra useful information to make sure your therapy is working as it should.

If your masculinisation is not going to plan then check your FAI and if it is high then you may need to adjust the dose and method of administration to optimise your care.

Normal Ranges (any gender)

Testosterone: less than 3 for feminising profile, more than 12 for masculinising profile

SGBH: 10-144 nmo/L – as the range varies widely, it is often difficult to interpret results with precision, so physical changes and personal goals are important to take into consideration.

FAI: 7-150

Free Androgen Index

Hormone therapy in gender-affirming care focuses on testosterone levels and physical response to treatment as a key factor in masculinisation. However, understanding both total testosterone levels and the Free Androgen Index (FAI) can provide a more comprehensive picture of hormonal balance and its effects on the body.

What is Testosterone?

Testosterone is a primary sex hormone, playing a crucial role in the development of reproductive tissues, as well as promoting secondary sexual characteristics such as increased muscle and bone mass, and the growth of body hair. In gender-affirming hormone therapy for transgender men and non-binary individuals, testosterone is used to induce masculinisation.

Total Testosterone Levels

When monitoring testosterone therapy, healthcare providers often measure total testosterone levels in the blood. This includes:

  • Bound Testosterone: Most testosterone in the body is bound to proteins like sex hormone-binding globulin (SHBG) or albumin. This testosterone is not biologically active.
  • Free Testosterone: A small percentage of testosterone circulates freely in the blood and is biologically active.

Total testosterone levels provide a broad overview of the amount of hormone present in the body, but they don’t always truly reflect the hormone’s activity.

Free Androgen Index (FAI)

The Free Androgen Index is a calculation that provides insight into the amount of free compared with biologically active testosterone. It is calculated by dividing the total testosterone by the SHBG concentration and then multiplying by a constant (usually 100).

Why FAI is Important

  • Active Testosterone Measurement: FAI helps estimate the fraction of circulating testosterone that is not bound to SHBG and is free to act on tissues.
  • Masculinisation Effects: In gender-affirming therapy, understanding the level of active testosterone can be important if changes associated with masculinisation are not occurring as expected.

Optimising Testosterone Levels

The goal is to achieve testosterone levels that fall within the typical male physiological range. This is often the primary focus initially but if masculinisation effects (like deepening of the voice, facial/body hair growth, changes in body fat distribution, etc.) are not as expected, despite optimal total testosterone levels, assessing the FAI becomes important.

Considering FAI in Hormone Therapy

  • Evaluating Masculinisation: If testosterone levels are optimised but masculinisation is not progressing, a high SHBG level might be binding too much testosterone, reducing its biological activity.
  • Adjusting Treatment: In these cases, making adjustments in therapy, such as changing the mode of testosterone administration or increasing doses or addressing factors that influence SHBG levels can help achieve effective masculinisation.

Sex Hormone-Binding Globulin (SHBG)

SHBG is a protein made by the liver which binds to the sex hormones and can stop their action. Having high levels of Sex Hormone-Binding Globulin (SHBG) can impact your body’s hormonal balance, particularly affecting the availability of hormones like testosterone and estrogen. If you have high SHBG, here are some steps you can take:

  1. Evaluate Medications: Certain medications can increase SHBG levels. Discuss with your doctor if you’re taking any medications that might affect SHBG and if alternatives are available.
  2. Dietary Adjustments: Diet plays a role in hormonal balance. Consider a diet rich in protein and healthy fats. Foods like lean meats, eggs, and nuts can be beneficial. Avoid excessive sugar and refined carbs, which can disrupt insulin levels and in turn affect SHBG.
  3. Exercise Regularly: Regular physical activity, especially strength training, can help in balancing hormone levels. It’s thought to have a positive effect on lowering SHBG, thus making more free testosterone available in the body.
  4. Manage Weight: Being overweight or underweight can affect hormone levels. Work towards maintaining a healthy weight.
  5. Stress Management: Chronic stress can lead to hormonal imbalances.
  6. Avoid Alcohol and Smoking: Excessive alcohol consumption and smoking can disrupt hormonal balance. Reducing or quitting these can help in managing SHBG levels.

Which medications can increase Sex Hormone-Binding Globulin (SHBG)?

  1. Estrogen-containing Medications: This includes oral contraceptives (birth control pills) and hormone replacement therapy (HRT) that contain estrogen. Estrogen can stimulate the liver to produce more SHBG.
  2. Thyroid Hormone Replacement: Medications like levothyroxine, used to treat hypothyroidism, can increase SHBG levels, especially in higher doses.
  3. Anticonvulsants: Certain antiepileptic drugs, such as phenytoin and carbamazepine, have been known to raise SHBG levels.
  4. Certain Antipsychotics: Some antipsychotic medications, especially those that have a significant impact on hormonal pathways, may contribute to increased SHBG levels.
  5. HIV Medications: Some antiretroviral drugs used in the treatment of HIV may affect SHBG levels.
  6. Tamoxifen: Used in the treatment of breast cancer, tamoxifen can increase SHBG levels.
  7. Clomiphene Citrate: A medication used to treat infertility, clomiphene can raise SHBG levels.


While total testosterone levels are a fundamental aspect of monitoring and adjusting hormone therapy for masculinisation, they don’t always tell the whole story. The Free Androgen Index offers additional insight into the biological activity of testosterone in the body. Both these measures should be considered in hormone therapy, particularly when the expected physical changes are not aligning with the measured testosterone levels. As always, hormone therapy should be tailored and adjusted, ensuring that it aligns with individual goals, health considerations, and the unique response of each person’s body to hormone treatment.

Further Reading:




Updated on January 31, 2024

Was this article helpful?

Related Articles

Request an article
If you would like some knowledge added to our knowledge base, send your suggestions here.
Request Knowledge