Estradiol is the most biologically active oestrogen and is the most abundant form of oestrogen in premenopausal women. Levels of estradiol in premenopausal women are highly variable throughout the menstrual cycle.  Estradiol levels are of value in the induction of ovulation, assessment of amenorrhoea, evaluation of testicular dysfunction or gonadal dysgenesis. They are also regularly used as part of fertility investigations and to determine suitable doses of hormones during individualised treatment protocols pre IVF.

A sustained reduction in estradiol levels results in reduced calcium resorption, accelerated loss of bone density and a subsequent increase in triglyceride levels. In patients with overt POI, they are at a higher risk for earlier onset cardiovascular disease and osteoporosis. Low levels indicate ovarian insufficiency, menopause, POI, PCOS, hypopituitarism, hypogonadism, severe eating disorders and genetic causes such as Turner syndrome.

Clinically significant increased levels can occur in with patients with ovarian or adrenal rumours, gynaecomastia, testicular tumours and adrenal hyperplasia and in children with precocious puberty in children; and warrant further investigation.