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Blood Test: Luteinizing Hormone (LH)

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.



The Procedure

A health professional will clean the skin surface with antiseptic, and place an elastic band (tourniquet) around the upper arm to apply pressure and cause the veins to swell with blood. Then a needle is inserted into a vein (usually in the arm inside of the elbow or on the back of the hand) and blood is withdrawn and collected in a vial or syringe.



What to Expect


Getting the Results

The blood sample will be processed by a machine, and results are usually available in a couple of days.



  • fainting or feeling lightheaded
  • pain associated with multiple punctures to locate a vein

Helping Your Child



If You Have Questions

If you have questions about the LH test, speak with your doctor.

Reviewed by: Yamini Durani, MD
Date reviewed: September 2014