Both luteinizing hormone (LH) and gonadotropin-releasing hormone (GnRH) are important in male and female reproduction. Their interaction is a vital part of the menstrual cycle and conception in women. They’re also important to the production of sperm cells in men.
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’s working correctly, it should cause LH to be released into the bloodstream. If it's not working correctly, the test can help doctors figure out underlying reasons for certain symptoms, such as low hormone levels.
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.
What Are Luteinizing and Gonadotropin-Releasing Hormones?
GnRH is a hormone produced in the hypothalamus region of the brain. GnRH moves through the bloodstream to the pituitary gland. There, it binds to certain receptors. Those receptors signal 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.
After ovulation, 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.
There are two main reasons why your doctor may order an LH response to GnRH test: 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’s called primary hypogonadism. When it centers in the pituitary gland and hypothalamus areas of the brain, it’s called central or secondary hypogonadism.
To treat hypogonadism, your doctor needs to know if it’s primary or secondary. The LH response to GnRH test can indicate where the problem occurs in your body.
Your doctor may also order an LH response to GnRH test to check 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 needs to take a sample of your blood. Then they’ll 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.
You’ll do the test 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. You may have a small amount of bruising where the needle was inserted. You can minimize it by putting pressure on the wound after the nurse removes the needle. In rare cases, you may experience phlebitis, an inflammation of your vein. It’s not a serious problem. You’ll just need to apply a warm compress to the needle site throughout the day.
Your doctor will tell you what to do before having your blood drawn for an LH response to GnRH test. You should tell your doctor if you have any bleeding disorders. 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. Your doctor will likely also ask that you don't eat or drink anything during the eight hours leading up to the blood draw.
Interpreting the LH response to GnRH test is very complicated. It considers gender, age, and weight. The results of the tests compare LH levels and FSH (follicle-stimulating hormone) levels over time.
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:
- pituitary tumors
- Kallmann syndrome
- irregular or absent periods
- hyperprolactinemia (having an excess of prolactin, the hormone that produces breast milk in women)
Your doctor will explain the results of your test to you. The values of the test can vary, depending on the laboratory that does the work.