The Free Androgen Index (FAI) is a medical measurement used to assess hormone levels in the body. It provides insight into the amount of active androgens, such as testosterone, that are available for use by the body’s tissues. This measurement helps healthcare providers understand an individual’s hormonal balance and can be important for diagnosing various conditions.
Understanding the Free Androgen Index
The Free Androgen Index is a calculated ratio that helps determine a person’s androgen status. Androgens are hormones that contribute to male characteristics, with testosterone being the most common. Total testosterone measures all testosterone in the blood, but not all of it is readily available for the body to use.
A significant portion of testosterone is bound to Sex Hormone Binding Globulin (SHBG), a protein primarily produced in the liver. SHBG binds tightly to sex hormones, carrying them throughout the blood. When testosterone is bound to SHBG, it is biologically inactive, meaning it cannot easily interact with cells.
The FAI provides a clearer picture of biologically available testosterone by accounting for SHBG. While some testosterone is weakly bound to albumin, SHBG-bound testosterone is largely unavailable. The FAI is calculated by dividing the total testosterone level by the SHBG level, often multiplied by 100 for a more manageable number.
Reasons for Testing the Free Androgen Index
A healthcare provider may recommend an FAI test when there are signs of abnormal androgen levels, which can manifest differently in men and women.
For women, symptoms suggesting an excess of androgens, also known as hyperandrogenism, often prompt this test. These symptoms can include hirsutism (excessive hair growth), acne, irregular menstrual cycles (including absent periods), and difficulty conceiving. Polycystic Ovary Syndrome (PCOS) is a common condition associated with elevated androgen levels in women, and the FAI can be a part of its diagnostic workup.
For men, a low FAI can indicate a testosterone deficiency, also known as hypogonadism. This condition can lead to symptoms such as reduced sex drive, erectile dysfunction, fatigue. Other signs include decreased muscle mass, muscle weakness, and breast development.
The FAI is typically part of a broader diagnostic workup, alongside other tests like total testosterone and gonadotropin levels, to provide a comprehensive assessment of a patient’s hormonal status.
Interpreting Free Androgen Index Results
Interpreting Free Androgen Index results requires careful consideration by a healthcare professional, as normal ranges can vary based on the laboratory and an individual’s age. For healthy adult men, typical FAI values might range from 30 to 150. In women, typical FAI values are generally lower, often between 7 and 10.
Elevated FAI levels in women often suggest hyperandrogenism. This can be indicative of conditions like Polycystic Ovary Syndrome (PCOS), which is the most common cause of high androgen levels in women. Symptoms associated with high FAI in women can include irregular or absent periods, weight gain, thinning hair, excessive body and facial hair growth (hirsutism), and acne.
A low FAI in men can indicate testosterone deficiency or hypogonadism. Symptoms associated with low FAI in men include a reduced sex drive, problems with erections, fatigue, decreased muscle mass and strength, and mood changes like depression. While a low FAI is less commonly the primary concern in women, very low levels might be observed in certain conditions, potentially leading to low libido, reduced bone mass, and fatigue.
FAI results should not be interpreted in isolation. A healthcare professional considers these results in the context of a patient’s symptoms, medical history, and other laboratory tests to reach an accurate diagnosis and determine appropriate management. For instance, if a high initial testosterone level is found, further confirmation by tandem mass spectrophotometry might be performed, which could delay FAI reporting.