LH response to GnRH is a test of the ability of the pituitary gland to appropriately respond to stimulation by a gonadotropin releasing hormone (GnRH, a hormone produced in the hypothalamus). This ability is assessed indirectly.

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 puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

For an infant or young child:

The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any continued bleeding.

Adults:

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 helps differentiate between primary (arising from the testicle or ovary) and secondary (originating in the hypothalamus or pituitary gland) hypogonadism. This test may be performed as part of the evaluation of gonadal failure associated with low testosterone levels in men or low estradiol (estrogen) levels in women.

Normal LH levels are:

• Children: < 2.0 IU/ml
• Male: 0.9 to 10.6 IU/ml
• Female; follicular: 1.1 to 11.1 IU/ml
• Female; mid-cycle: 17.5 to 72.9 IU/ml
• Female; luteal; 0.4 to 15.1 IU/ml
• Female; post menopausal: 6.8 to 46.6 IU/ml

Note: IU/ml = international units per milliliter.

• An excess LH response suggests primary gonadal failure (the problem is within the ovaries or testes).
• A reduced LH response suggests hypothalamic or pituitary disease.
• A gonadotropin deficiency can be present at birth as a congenital or hereditary disorder.
• Kallmann's syndrome is a rare congenital disease characterized by gonadotropin deficiency caused by GnRH deficiency.
• Acquired defects of GnRH production are more common (hyperprolactinemia or amenorrhea may be caused by inhibition of GnRH release, possibly due to increased hypothalamic dopamine or prolactin).
• Anorexia nervosa and starvation inhibit GnRH release.
• A gonadotropin deficiency may be a relatively early problem in patients with large pituitary adenomas (tumors).
• A gonadotropin deficiency also occurs in patients with polyglandular endocrine deficiency (an autoimmune disorders ) and in people with hemochromatosis.

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

GnRH, which stands for gonadotropin releasing hormone, is secreted from the hypothalamus. It is also called luteinizing hormone-releasing hormone or LHRH.

GnRH stimulates the creation and release of LH (luteinizing hormone) and FSH (follicle-stimulating hormone). After puberty GnRH secretion, as well as LH and FSH secretion, becomes pulsatile (meaning rhythmic). Having a steady infusion of GnRH, however, causes inhibition (stopping the release of) LH and FSH.

In women, estrogen levels rise during the menstrual cycle until there is enough estrogen present to stimulate the release of GnRH and LH. This is the phenomenon that causes the LH surge prior to ovulation.

Progesterone in high concentrations (for example, during the luteal phase of the menstrual cycle or during pregnancy) reduces GnRH pulses and also reduces the response of the pituitary gland to GnRH.

In men, testosterone reduces LH pulses, probably by reducing the release of GnRH. Inhibin, a hormone produced by the testes and ovaries, is probably the major inhibitor of FSH release.

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.