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Free Androgen Index (FAI)

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The Free Androgen Index (FAI) is a marker used to assess androgen status in an individual. This index is calculated based on total testosterone and sex hormone-binding globulin (SHBG) levels.

  • Most testosterone in the body is not in its free form but is bound to proteins.
  • The Free Androgen Index provides information about the level of free testosterone available in the body.

    Effects of Altered Free Androgen Index

  • Low FAI in men may manifest as chronic fatigue, erectile dysfunction, osteoporosis, and loss of secondary sexual characteristics.
  • High FAI in women is commonly associated with hirsutism (excessive hair growth) and polycystic ovary syndrome (PCOS).
  • The analysis is performed on a blood sample drawn from a vein.
  • To determine the Free Androgen Index, tests for total testosterone and SHBG are required.
  • Fasting is required for 8–10 hours before the test.
  • Reproductive dysfunction
  • Alopecia (hair loss)
  • Malignant adrenal tumors
  • Acne, oily seborrhea, and related skin conditions

Causes of Increased Free Androgen Index

A high FAI indicates excess bioactive testosterone in the bloodstream.

  • In men, excess testosterone may lead to:

    • Increased aggression
    • Cystic acne
    • Excessive body hair growth
    • However, adult men often do not experience noticeable symptoms.

  • In women, excess testosterone may cause:

    • Abnormal hair growth (hirsutism)
    • Obesity
    • Voice deepening
    • Menstrual irregularities

  • In children, high testosterone may lead to:

    • Premature puberty

Specific Causes of High FAI:

  • Polycystic ovary syndrome (PCOS)
  • Testosterone-secreting tumors
     

    Causes of Decreased Free Androgen Index

    A low FAI may indicate insufficient testosterone activity.

  • In adult men, low testosterone levels may cause:

    • Loss of muscle mass
    • Fatigue, weakness, and depression
    • Decreased libido and erectile dysfunction
    • Gynecomastia (breast tissue development in men)

  • In boys, low testosterone may result in:

    • Delayed puberty
    • Lack of secondary sexual characteristics (e.g., deep voice, pubic and facial hair growth)

  • In women, low testosterone is not typically a concern, though it may affect sexual function.

  • Specific Causes of Low FAI:

  • Hypogonadism
  • Testicular damage
  • Testicular cancer
  • Type 2 diabetes
  • Obesity
  • Chronic liver disease
  • Chronic kidney disease