Description

The Androgen Index, often referred to as the Free Androgen Index (FAI), is a calculation used to assess the levels of free (bioavailable) androgens, particularly testosterone, in the body. It is commonly used to evaluate androgen status in both men and women and can help diagnose conditions such as polycystic ovary syndrome (PCOS), androgen deficiency, or hyperandrogenism.

Calculation of Free Androgen Index

The Free Androgen Index is calculated using the following formula:

FAI=(Total TestosteroneSHBG)×100\text{FAI} = \left( \frac{\text{Total Testosterone}}{\text{SHBG}} \right) \times 100FAI=(SHBGTotal Testosterone​)×100

Where:

• Total Testosterone: The total amount of testosterone in the blood.
• SHBG (Sex Hormone-Binding Globulin): A protein that binds to sex hormones, including testosterone, reducing their bioavailability.

Interpretation

• Normal Range: The reference range for FAI can vary depending on the laboratory and population, but generally:
  • For men: 30-150
  • For women: 0.5-6.5
• High FAI: Indicates increased levels of free androgens. In women, this may suggest conditions like PCOS or adrenal hyperplasia. In men, it may indicate androgen-secreting tumors or anabolic steroid use.
• Low FAI: Indicates decreased levels of free androgens. In men, this could suggest hypogonadism or androgen deficiency. In women, it might be associated with conditions such as hypopituitarism or chronic illness.

Clinical Significance

• PCOS: In women, a high FAI is often used as a diagnostic marker for PCOS, characterized by irregular menstrual cycles, hirsutism, and ovarian cysts.
• Androgen Deficiency: In men, a low FAI can help diagnose androgen deficiency, which may cause symptoms like reduced libido, fatigue, and decreased muscle mass.

Testing

• Blood Test: Blood samples are taken to measure total testosterone and SHBG levels. The FAI is then calculated using these values.
• Preparation: Patients might need to fast before the blood draw, and it’s important to inform the healthcare provider of any medications or supplements being taken.

Follow-Up

• Further Testing: Depending on the results, additional tests may be required, such as direct measurement of free testosterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH), or imaging studies.
• Treatment: Treatment options vary based on the underlying condition and may include hormonal therapies, lifestyle changes, or other medical interventions.

The Free Androgen Index is a useful tool in the assessment of androgen-related disorders and provides valuable insights into an individual’s hormonal status.