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LH response to GnRH
Definition
LH response to GnRH is a blood test to help determine if your pituitary gland can correctly respond to gonadotropin releasing hormone (GnRH). GnRH is a hormone produced in the hypothalamus.
Alternative Names
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, other blood samples are taken so that LH can be measured.
For information on how the blood sample is taken, see: Venipuncture
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, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the Test is Performed
This test is used to tell the difference between primary and secondary hypogonadism , a condition in which the sex glands produce little or no hormones. In men, the sex glands (gonads) are the testes. In women, the sex glands are the ovaries.
- 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 evaluate low testosterone levels in men or low estradiol levels in women.
Normal Results
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 excessive LH response suggests a problem within the ovaries or testes.
A reduced LH response suggests a problem with the hypothalamus or pituitary gland.
Abnormal results may also be due to:
- Large pituitary tumors
- Endocrine deficiency
- Hemochromatosis
- Kallmann syndrome
- Hyperprolactinemia
- Amenorrhea
- Anorexia nervosa
- Starvation
- Obesity
Risks
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)
Considerations
In women, estrogen levels rise during the menstrual cycle until there is enough estrogen present to stimulate the release of GnRH and lutenizing hormone (LH).
Progesterone in high concentrations (for example, during the luteal phase of the menstrual cycle or during pregnancy) reduces the response of the pituitary gland to GnRH.
References
Webster RA. Reproductive function and pregnancy. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. Philadelphia, Pa: Saunders Elsevier; 2006:chap 25.
Ferri FF. Laboratory tests and interpretation of results. In: Ferri FF, ed. Ferri’s Clinical Advisor 2012. 1st ed. Philadelphia, Pa: Mosby Elsevier; 2011:section IV.
Reviewed By: Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine; Susan Storck, MD, FACOG, Chief, Eastside Department of Obstetrics and Gynecology, Group Health Cooperative of Puget Sound, Redmond, Washington; Clinical Teaching Faculty, Department of Obstetrics and Gynecology, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
