LH response to GnRH
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.
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.
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 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 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. A bandage may be applied to the puncture site if there is any continued bleeding.
How to prepare for the test
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:
- Infant test or procedure preparation (birth to 1 year)
- Toddler test or procedure preparation (1 to 3 years)
- Preschooler test or procedure preparation (3 to 6 years)
- Schoolage test or procedure preparation (6 to 12 years)
- Adolescent test or procedure preparation (12 to 18 years)
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 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
- 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 (hyperprolactinemia or amenorrhea 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.
- 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
by Martin A. Harms, M.D.
All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.