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LH response to GnRH
Definition:
A test that assesses 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.

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 in the serum.

Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (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 tourniquet 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.

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. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
How to prepare for the test:
Adults:
No special preparation is necessary.

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
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 in to help differentiate primary (testicular or ovarian) from secondary (hypothalamic or pituitary) hypogonadism. This test may be performed as part of the evaluation of gonadal failure associated with low testosterone levels in men or low estradiol (see Estradiol test) levels in women.
Normal Values:
LH level
  • 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.
What abnormal results mean:
  • An excess LH response is indicative of 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, for example, hyperprolactinemiaamenorrhea may be caused by inhibition of GnRH release, possibly mediated by increased hypothalamic dopamine or prolactin.
  • Anorexia nervosa and starvation inhibit GnRH release as well.
  • A gonadotropin deficiency may be a relatively early defect in patients with large pituitary adenomas (tumors).
  • A gonadotropin deficiency also occurs in patients with polyglandular endocrine deficiency (presumably one of the autoimmune disorders) and in people with hemochromatosis.
What the risks are:
  • 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
Special considerations:
GnRH (also called luteinizing hormone-releasing hormone, LHRH, or gonadotropin releasing hormone) is a peptide hormone secreted from the hypothalamus. GnRH stimulates the synthesis and release of LH (luteinizing hormone) and FSH (follicle-stimulating hormone). After puberty the secretion of GnRH, and also of LH and FSH, becomes pulsatile (rhythmic). However, continuous infusion of GnRH results in the inhibition of LH and FSH release.

In women, estrogen levels increase during the menstrual cycle until a level is reached at which a positive feedback signal stimulates GnRH and LH release -- a phenomena that is responsible for the LH surge prior to ovulation. Progesterone in high concentrations (for example, during the luteal phase of the menstrual cycle or during pregnancy) decreases the frequency of GnRH pulsations and also the response of the pituitary to GnRH. In men, testosterone decreases the frequency of LH pulses, probably by a direct effect on GnRH release. Inhibin, a peptide 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.
Review Date: 8/9/2001
Reviewed By: Peter Chen, M.D., Department of Obstetrics & Gynecology, Univrsity of Pennsylvania Medical Center, Philadelphia, PA. Review provided by VeriMed Healthcare Network.
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