DefinitionLH response to GnRH is a blood test to indirectly determine the pituitary gland's ability to appropriately respond to gonadotropin releasing hormone (GnRH), a hormone produced in the hypothalamus.Alternative NamesLuteinizing hormone response to gonadotropin-releasing hormoneHow the test is performedA blood sample is drawn prior to an injection of GnRH. After a specified time, other blood samples are drawn so that LH can be measured.Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.Next, the health care provider gently inserts a needle into the vein.