This test measures free and total testosterone and sex hormone-binding globulin (SHBG). Testosterone testing is important to diagnose conditions such as hypogonadism, which can lead to symptoms like decreased libido, fatigue, and muscle weakness. High testosterone levels can be associated with conditions like polycystic ovary syndrome (PCOS) in women or adrenal tumors in both men and women. It is also vital when monitoring hormone replacement therapy.