LH response to GnRH blood test

Definition

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.

Alternative Names

Luteinizing hormone response to gonadotropin-releasing hormone

How the Test is Performed

A blood sample is taken, and then you are given a 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. Afterward, there may be some throbbing or a slight bruise. This soon goes 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 is 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 also be done to check for the reason why there is a:

• Low testosterone level in men
• Low estradiol level 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 health care provider 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)
• Obesity

Risks

There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

Other risks related to having blood drawn are slight, but may include:

• Excessive bleeding
• Fainting or feeling lightheaded
• Multiple punctures to locate veins
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

References

Guber HA, Oprea M, Russell YX. Evaluation of endocrine function. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 25.

Kaiser U, Ho K. Pituitary physiology and diagnostic evaluation. In: Melmed S, Auchus, RJ, Goldfine AB, Koenig RJ, Rosen CJ, eds. Williams Textbook of Endocrinology. 14th ed. Philadelphia, PA: Elsevier; 2020:chap 8.