LH response to GnRH blood test
LH response to GnRH is a blood test to help determine if your pituitary gland can correctly respond to gonadotropin releasing hormone (GnRH). LH stands for luteinizing hormone.
Luteinizing hormone response to gonadotropin-releasing hormone
How the test is performed
A blood sample is taken, and then you are given an shot of GnRH. After a specified time, more blood samples are taken so that LH can be measured.
How to prepare for the test
No special preparation is necessary.
How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging sensation. Afterward, there may be some throbbing or a slight bruise. These soon go away.
Why the test is performed
GnRH is a hormone made by the hypothalamus gland. LH is made by the pituitary gland. GnRH causes (stimulates) the pituitary gland to release LH.
This test is used to tell the difference between primary and secondary hypogonadism. Hypogonadism a condition in which the sex glands make little or no hormones. In men, the sex glands (gonads) are the testes. In women, the sex glands are the ovaries.
Depending on the type of hypogonadism:
- Primary hypogonadism starts in the testicle or ovary
- Secondary hypogonadism starts in the hypothalamus or pituitary gland
This test may be also be done to check:
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.
What abnormal results mean
An increased LH response suggests a problem in the ovaries or testes.
A reduced LH response suggests a problem with the hypothalamus gland or pituitary gland.
Abnormal results may also be due to:
- Pituitary gland problems, such as release of too much hormone (hyperprolactinemia)
- Large pituitary tumors
- Decrease in hormones made by the endocrine glands
- Too much iron in the body (hemochromatosis)
- Eating disorders, such as anorexia
- Recent significant weight loss, such as after bariatric surgery
- Delayed or absent puberty (Kallmann syndrome)
- Lack of periods in women (amenorrhea)
What the risks are
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks related to having blood drawn are rare but may include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
Borawski D, Bluth MH. Reproductive function and pregnancy. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, Pa: Elsevier Saunders; 2011:chap 25.
Gruber HA, Farag AF. Evaluation of endocrine function. In: McPherson RA, Pincus MR, eds. Henry’s Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, Pa: Elsevier Saunders; 2011:chap 24.
Melmed S, Kleinberg D, Ho K. Pituitary physiology and diagnostic evaluation. In: Melmed S, Polonsky KS, Larsen PR, Kronenberg HM, eds. Williams Textbook of Endocrinology. 12th ed. Philadelphia, Pa: Elsevier Saunders; 2011: chap 8.