Estrone (E1)

Estrone (E1) is one of the three main estrogens, alongside estradiol (E2) and estriol (E3). It is a weaker estrogen than estradiol, but it can be converted to and from estradiol, so the two are linked. Before menopause, the ovaries make mostly estradiol, and estrone is the minor player. After menopause, when the ovaries stop making estradiol, the balance shifts: estrone becomes the body's predominant estrogen. It is produced not by the ovaries but by the conversion of adrenal androgens in fat tissue — which is why body fat influences estrogen levels after menopause, and why higher body fat raises estrone. Estrone is a specialist test rather than a routine one. It is measured in the assessment of estrogen status in specific situations: characterising estrogen after menopause, investigating some causes of estrogen excess (for example an estrogen-producing tumour, or high conversion in obesity), monitoring certain hormone therapies, and in the work-up of some fertility and hormone disorders. Because it fluctuates with sex, menstrual cycle phase and menopausal status, and because estradiol is usually the more clinically useful estrogen to measure, estrone is interpreted in context and alongside estradiol and FSH rather than on its own.

• Higher body fat / obesity — fat tissue converts adrenal androgens into estrone.
• An estrogen-producing tumour — a rare but important cause of estrogen excess.
• Estrogen (hormone) therapy — an expected effect during treatment.
• Relative estrogen excess after menopause — relevant to some hormone-related conditions.

• Low overall estrogen — as in ovarian failure or hypogonadism, when both estradiol and estrone are low.
• Very low body fat — less tissue available to make estrone.
• Suppression of the ovaries or pituitary–gonadal axis.