What Is the Free Androgen Index?

The free androgen index measures normal or abnormal levels of testosterone by calculating the ratio of testosterone to a sex hormone-binding protein defined as globulin. The test is used to treat testosterone deficiency in men, and low or elevated levels in women. Free androgen index results might help doctors treat low libido, osteoporosis, and ovarian disorders. The index is also used in fertility testing.

Testosterone is secreted by the testes in men, with most of the hormone binding to protein, which aids its delivery throughout the body. Men who test low on this index might suffer from erectile dysfunction and a low sex drive. They may also feel tired and lose bone mass.

Women also produce testosterone in the ovaries and adrenal glands, but in small amounts. The free androgen index tests for overproduction of testosterone in women who show signs of elevated male sex hormones. When levels spike, women may begin growing facial and body hair, experience irregular menstrual cycles, and cease ovulating on a predictable schedule. These disorders might make conceiving difficult for women in their child-bearing years.

High levels of testosterone shown on the free androgen index might also indicate polycystic ovary syndrome, a hormonal disorder linked to excess androgen. The ovaries commonly become enlarged, and numerous small cysts might develop. More than half of women diagnosed with polycystic ovary syndrome are also obese, with high levels of androgen. The disorder is also connected to diabetes, stroke, and heart disease.

Testosterone in the human body is measured in three ways. Free testosterone is not bound to any protein, while some testosterone might be weakly bound to globulin. The free androgen index determines the ratio of free testosterone to tightly bound or weakly bound sex hormone-binding proteins. This measurement reveals if androgen levels fall into the normal range.

Postmenopausal women commonly show increased androgen levels as estrogen declines during menopause. The condition might contribute to loss of sexual desire and osteoporosis, a disorder that causes the bones to become thin and brittle. Some women use hormone replacement therapy (HRT) that contains estrogen and testosterone to address these risks. Hormones are available in oral form, androgen implants, and patches.

Side effects of HRT include fluid retention and possibly lower levels of healthy cholesterol that might protect against heart disease. Studies on the effects of estrogen and testosterone medication on breast cancer are mixed. Some studies show an increased risk of developing breast cancer in women using HRT, while other research shows no connection between hormone supplements and breast cancer.