Both luteinizing hormone (LH) and gonadotropin releasing hormone (GnRH) are important in male and female reproduction. Their interaction with each other is a necessary part of the menstrual cycle and conception in women, as well as in the production of sperm cells in men. A test of the response of LH to GnRH can help doctors determine underlying reasons for certain symptoms in their patients, such as low hormone levels.
GnRH is a hormone that is produced in the hypothalamus region of the brain. Once produced, GnRH moves through the bloodstream to the pituitary gland. There, it binds to certain receptors, which signals the pituitary gland to create two more hormones: LH and follicle-stimulating hormone (FSH).
In women, FSH goes on to stimulate the growth of eggs in the ovaries. This leads to the production of estrogen, another hormone, which sends a signal back to the pituitary gland to slow the releasing of FSH and to make more LH. The change leads to ovulation and a drop in both LH and FSH.
Once ovulation has occurred, the empty follicle in the ovary begins producing yet another hormone, progesterone, which is needed to maintain a pregnancy. If ovulation does not lead to pregnancy, the cycle goes back to the beginning.
In men, GnRH stimulates the release of LH from the pituitary gland. LH then binds to receptor cells in the testicles to begin the production of sperm cells.
An “LH response to GnRH test” is a blood test that tells your doctor whether or not your pituitary gland is functioning correctly when GnRH binds to its receptors. If it is functioning correctly, it should cause LH to be released into the bloodstream.
There are two main reasons why your doctor may order an LH response to GnRH test. It is used to evaluate hormone levels and to confirm primary or secondary hypogonadism.
Hypogonadism occurs when the sex glands in either men (testes) or women (ovaries) produce little or no hormones. It can be caused by genetic disorders like Turner, Klinefelter, and Kallmann syndromes. It can also be caused by tumors. When hypogonadism centers on the testes or ovaries, it is called primary hypogonadism. When it centers in the pituitary gland and hypothalamus areas of the brain, it is called central or secondary hypogonadism.
To treat hypogonadism, your doctor needs to know if it is primary or secondary. The LH response to GnRH test can indicate where the problem arises in your body.
Your doctor may also order an LH response to GnRH test to evaluate the level of certain hormones in your body. It can give a doctor an idea of testosterone levels in male patients and estradiol levels (an important form of estrogen) in female patients.
To perform an LH response to GnRH test, your doctor will need to take a sample of your blood. Then your doctor will give you a shot of GnRH. Over a period of time, typically 20 minutes and 60 minutes after the injection, additional blood samples will be drawn so the luteinizing hormone (LH) can be measured.This will likely be done in a lab in your doctor’s building or right in the office. A nurse or medical assistant will take your blood by inserting a needle into a vein in the inside of your arm. A tube connected to that needle will collect a small amount of blood.
There are very few risks associated with having blood drawn. A small amount of bruising may occur where the needle was inserted, but if you put pressure on it after the needle is withdrawn, you can minimize this. In rare cases, you may experience phlebitis, an inflammation of your vein. It is not a serious problem and you will probably be directed to apply a warm compress to the needle site throughout the day. You should tell your doctor if you have any bleeding disorders before having blood drawn.
Your doctor will tell you what to do before having your blood drawn for an LH response to GnRH test. You may need to stop taking certain medications before the test, such as birth control and any other hormone pills. They may interfere with your results. It is likely that your doctor will also ask that you not eat or drink anything during the eight hours leading up to the blood draw.
Your doctor can tell you when to expect your results. The values of the test can vary depending on the laboratory that does the work. Your doctor will explain your results to you.
Interpreting the LH response to GnRH test test is very complicated and takes into consideration gender, age, and weight. The results of the tests compare LH levels and FSH (follicle-stimulating hormone) levels over time. (BILM)
When the LH response is higher than normal, it may indicate primary hypogonadism, or a problem with the ovaries or testes. When the response is too low, it may indicate secondary hypogonadism, or an issue with the pituitary gland and hypothalamus.
Other reasons for abnormal results include anorexia, obesity, pituitary tumors, Kallmann syndrome, irregular or absent periods, or hyperprolactinemia, which is means having an excess of prolactin, the hormone that produces milk in women.