LH RESPONSE TO GNRH - This test measures the level of luteinizing hormone in the blood after an injection of gonadotropin releasing hormone (GNRH), normally produced in the hypothalamus. This will test the ability of the pituitary gland to respond by measuring one of the pituitary glands byproducts, luteinizing hormone. This test is used to differentiate hypogonadism (ovary or testes) into primary hypogonadism (problem is with the ovary or testes) or secondary hypogonadism (problem is with the pituitary gland or the hypothalamus).