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.

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.

No special preparation is necessary.

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.

This test is used to tell the difference between primary and secondary 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 evaluate low testosterone levels in men or low estradiol levels in women.

• Children: less than 2.0 international units per milliliter (IU/mL)
• Male: 0.9 to 10.6 IU/mL
• Female; follicular phase of the menstrual cycle: 1.1 to 11.1 IU/mL
• Female; mid-cycle: 17.5 to 72.9 IU/mL
• Female; luteal phase of the menstrual cycle; 0.4 to 15.1 IU/mL
• Female; postmenopause: 6.8 to 46.6 IU/mL

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

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

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)

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.