Testosterone, Free and Weakly Bound, with Total Testosterone, LC/MS-MS

This blood test measures the total amount of testosterone in your body as well as the portion that is actively available to your cells, called 'free' and 'weakly bound' testosterone. Testosterone is an important hormone for both men and women, affecting energy, muscle, bone strength, sexual function, and mood. The test uses a highly accurate laboratory method called LC/MS-MS to give precise results, which is especially helpful when standard tests might be misleading. Your doctor uses these results alongside your symptoms and other lab tests to understand whether your testosterone levels are in a healthy range for your age and sex. Abnormal levels can have many causes and always require further evaluation by a healthcare provider.

When elevated: Elevated free and total testosterone may indicate androgen excess states such as polycystic ovary syndrome, congenital adrenal hyperplasia, adrenal or gonadal androgen-secreting tumors, or exogenous androgen use. In males, supraphysiologic levels may suggest exogenous testosterone administration or anabolic steroid use. Elevated androgens in females are associated with hirsutism, acne, menstrual irregularity, and virilization. When low: Low free and total testosterone in males is consistent with primary hypogonadism (testicular failure) or secondary hypogonadism (hypothalamic-pituitary dysfunction), and is associated with symptoms including decreased libido, erectile dysfunction, fatigue, reduced muscle mass, and osteoporosis. In females, low testosterone may contribute to decreased libido, fatigue, and reduced bone density, though clinical thresholds are less well established. Low values may also reflect critical illness, glucocorticoid excess, or significant nutritional deficiency.

Free and bioavailable testosterone drive muscle protein synthesis, recovery, and performance adaptations to training—making this panel more informative than total testosterone alone for assessing hormonal response to exercise. Athletes with high SHBG (from endurance training, low body fat, or other factors) may have normal total testosterone but reduced bioavailable testosterone, potentially limiting strength and hypertrophy gains; LC/MS-MS accuracy helps distinguish true hormone status from false reassurance.