What It Is
Luteinizing hormone (LH) plays an important role in sexual development and is produced
by the pea-sized pituitary gland in the brain. An LH test measures the level of this
hormone in the bloodstream.
In kids, LH levels are high right after birth, but then fall, remaining low until
puberty approaches (usually between ages 10 and 14). At this time the hypothalamus,
an almond-sized area of the brain that links the nervous system with the hormone-producing
endocrine system, releases gonadotropin-releasing hormone (GnRH) that starts the changes
of puberty. GnRH signals the pituitary gland to release two puberty hormones into
the bloodstream: LH and follicle stimulating hormone (FSH).
In boys, LH and FSH work together to get the testes to begin producing testosterone,
the hormone responsible for the physical changes of puberty and the production of
sperm.
In girls, LH and FSH prompt the ovaries to begin producing the hormone estrogen,
which causes a girl's body to mature and prepares her for menstruation.
Because LH and FSH work so closely with each other, doctors often perform these
tests together, as well as tests for testosterone (the major male sex hormone) and
estradiol (a form of estrogen, the major female sex hormone). Taken together, the
results can often provide a more complete picture of a child's sexual maturation,
and the well-being of the glands that produce these hormones.
Why It's Done
Doctors may order an LH test if a boy or girl appears to be entering puberty much
earlier or much later than expected. High levels are associated with precocious (early)
puberty, while low levels may indicate a delay in sexual development.
The test may also be used to check for damage or disease of the testes or ovaries,
pituitary gland, or hypothalamus.
In adults and teens, LH levels can also help doctors evaluate fertility issues
and menstrual problems.
Preparation
No special preparations are needed for this test. On the day of the test, having
your child wear a T-shirt or short-sleeved shirt can make things easier for the technician
drawing the blood.