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LH Response to GNRH

Definition

LH response to GnRH is a blood test to indirectly determine the pituitary gland's ability to appropriately respond to gonadotropin releasing hormone (GnRH), a hormone produced in the hypothalamus.

Alternative Names

Luteinizing hormone response to gonadotropin-releasing hormone

How the test is performed

A blood sample is drawn prior to an injection of GnRH. After a specified time, other blood samples are drawn so that LH can be measured.

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

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 Values

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

What abnormal results mean

An excessive LH response suggests that gonadal failure is due to 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:

  • Gonadotropin deficiency, may be seen in patients with:
    • Large pituitary tumors
    • Endocrine deficiency
    • Hemochromatosis
  • Kallmann syndrome
  • Hyperprolactinemia
  • Amenorrhea
  • Anorexia nervosa
  • Starvation
  • Obesity

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)

Special 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 2009. 1st ed. Philadelphia, Pa: Mosby Elsevier; 2009:section IV.

Review Date: 7/29/2009

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