Testosterone, Free, Bioavailable and Total, MS

This blood test measures testosterone—the main 'male hormone' present in both men and women—in three different ways using a highly precise laboratory technique called mass spectrometry. 'Total' testosterone measures all the testosterone in your blood, while 'free' and 'bioavailable' testosterone measure the portions your body can actually use. Because much of the testosterone in your blood is bound to proteins and unavailable to your cells, measuring all three fractions gives your doctor a more complete picture of your hormone status. This test helps evaluate symptoms like fatigue, low sex drive, irregular periods, excess hair growth, or infertility. Your results should always be discussed with your healthcare provider alongside your symptoms and other test results.

When elevated: Elevated total and free testosterone may indicate androgen excess states such as polycystic ovary syndrome (PCOS) in women, congenital adrenal hyperplasia, androgen-secreting tumors (adrenal or gonadal), or exogenous androgen use. In men, supraphysiologic levels raise concern for exogenous testosterone or anabolic steroid use. Elevated androgens in women are associated with hirsutism, acne, menstrual irregularity, and virilization. When low: Low free and total testosterone in men is consistent with hypogonadism, which may be primary (testicular failure) or secondary (hypothalamic-pituitary dysfunction). In women, low testosterone may contribute to reduced libido, fatigue, and decreased bone density, though clinical significance remains an area of ongoing research. Low bioavailable testosterone despite normal total testosterone suggests elevated SHBG as the underlying mechanism.

Testosterone supports muscle protein synthesis, bone density, recovery, and red blood cell production—all critical for athletic performance and training adaptation. Fractionated measurement is particularly useful for athletes monitoring hormonal response to heavy training, evaluating recovery status, or assessing whether changes in body composition or SHBG (influenced by diet, training intensity, and body fat) are affecting testosterone availability independent of total levels.