Androstenedione is a steroid which serves as a major precursor for testosterone and estrone. Its clinical interest derives from the fact that it is often elevated in cases of abnormal hair growth (hirsutism) and virilization.
Unlike the adrenal androgens dehydroepiandrosterone and its sulfate, circulating androstenedione originates both from the adrenals and from the ovaries.
Plasma levels increase steadily from about the seventh year of life, then gradually decline after the third decade. Androstenedione exhibits a diurnal variation, being highest in the morning, and also a cyclical variation during the menstrual cycle, being highest near midcycle. During pregnancy, there is an increase in the plasma level.