A DHEAS (Dehydroepiandrosterone Sulfate) test is a blood test measuring levels of this adrenal hormone, crucial for producing testosterone and estrogen, to check adrenal gland function, diagnose conditions like PCOS, adrenal tumors, Congenital Adrenal Hyperplasia, and investigate early puberty or signs of virilization in females. The test helps doctors understand hormonal imbalances, often used alongside other sex hormone tests, and fasting (especially from biotin supplements) might be needed before the morning blood draw.