Diagnostic Blood Test: Estradiol, Sensitive (LC/MS-MS) (also known as Estradiol, Ultra Sensitive) Estradiol or E2 is the principle estrogen in men and women. Estradiol plays important roles in neuroprotection, fertility, metabolism, and anabolism. Imbalanced levels of Estradiol may be associated with erectile dysfunction, low libido, gynecomastia (the growth of breast tissue), hair loss, reduced muscle strength, or low energy levels. The Estradiol, Sensitive test can more accurately measure levels of estradiol in men and post-menopausal women, who typically have lower levels of this hormone.