Luteinizing Hormone (LH) Test: What It Is and Why It’s Important

LH is a hormone that’s produced in the pituitary gland. The pituitary gland is located at the base of the brain, and it’s roughly the size of a pea. If you’re a female, LH is an important part of your menstrual cycle. It works with follicle-stimulating hormone (FSH), which is another gonadotropin made in the pituitary gland. FSH stimulates the ovarian follicle, causing an egg to grow. It also triggers the production of estrogen in the follicle.

The rise in estrogen tells your pituitary gland to stop producing FSH and to start making more LH. The shift to LH causes the egg to be released from the ovary, a process called ovulation. In the empty follicle, cells proliferate, turning it into a corpus luteum. This structure releases progesterone, a hormone necessary to maintain pregnancy. If pregnancy doesn’t occur, the levels of progesterone drop off and the cycle begins again.

If you’re a male, your pituitary gland also produces LH. The hormone binds to receptors in certain cells in your testes called Leydig cells. This leads to the release of testosterone, a hormone that’s necessary for producing sperm cells.

An LH blood test measures the amount of LH in your bloodstream. If you’re a woman, the amount of this hormone in your bloodstream varies with age and throughout the menstrual cycle. It also changes with pregnancy. If a doctor orders a test for LH related to fertility, a woman may need multiple tests to track the rising and falling hormone levels. LH levels can also be measured by analyzing a urine sample.

If you’re a man, your doctor can order an LH test to establish a baseline LH level. Your doctor can also measure your LH level after giving you an injection of gonadotropin releasing hormone (GnRH). Measuring LH after receiving this hormone can tell your doctor if you have a problem with the pituitary gland or with another part of your body.

There are many reasons for your doctor to request an LH blood test. Levels of LH relate to menstrual issues, fertility, and the onset of puberty.

Examples of instances when a doctor may order an LH blood test include:

• a woman is having difficulty getting pregnant
• a woman has irregular or absent menstrual periods
• it’s suspected that a woman has entered menopause
• a man has signs of low testosterone levels, such as low muscle mass or decrease in sex drive
• a pituitary disorder is suspected
• a boy or girl appears to be entering puberty too late or too soon

Your doctor may order the LH blood test in coordination with other hormone measurements, such as testosterone, progesterone, FSH, and estradiol.

Menstrual cycle and menopause

If you have absent or irregular periods, your doctor may want to determine the amount of LH in your bloodstream to find an underlying cause. LH levels should rise after menopause because your ovaries no longer function and take cues from LH.

Fertility

Your doctor may order an LH blood test if you’re having difficulty conceiving. LH levels can indicate a problem with the supply of eggs in a woman’s ovaries and a man’s sperm count, both of which affect fertility.

Puberty

For a younger person, a doctor may order an LH blood test to find the underlying causes for delayed or early puberty. A doctor will consider if a person is or isn’t showing signs of puberty. These include breast growth and menstruation in girls, testicle and penis growth in boys, and pubic hair growth in both boys and girls.

Pregnancy

A test of LH levels in the urine can be used to determine when you’re ovulating. When LH levels start to increase, this can indicate ovulation will likely occur within one to two days. These types of tests can be done at home and are often used to enhance the chances of conceiving. It’s important to note that this is accomplished with a urine test and not a blood test.

To administer an LH blood test, a health professional will draw a small amount of blood from you, most likely from your arm. The short procedure will be done in your doctor’s office or at a lab. The sample will then be analyzed for LH levels.

To draw blood, a health professional will wrap your upper arm with an elastic band to make your veins easier to see. They’ll disinfect the skin and insert a needle into a vein on the inside of your arm. A tube attached to the needle will collect a small sample of your blood. The process is short and mostly painless.

Your doctor may request that you have samples of blood drawn each day for several days. Because the amount of LH in the blood varies with your menstrual cycle, a few samples may be necessary to get an accurate measurement of your LH levels.

There aren’t many risks associated with having blood drawn. The needle site may bruise afterwards, but if you put pressure on it with a bandage, you can reduce this possibility.

Phlebitis, while rare, may occur when blood is drawn. This is when the vein becomes inflamed after blood is taken. If it occurs, your healthcare provider will likely have you apply a warm compress to the vein throughout the day. If you have any kind of bleeding disorder, make sure to tell your doctor to avoid complications from having blood drawn.

Your doctor should give you exact directions to prepare for your blood test. You may be told to stop taking certain medications that can affect the results, so be sure to inform your doctor of all medications and supplements you take. If you’re a woman, you may need to stop taking birth control or other hormone pills for up to four weeks before the test. Your doctor will also want to know the date of your last period.

As with many blood draws, you may be asked to avoid eating or drinking for up to eight hours leading up to the test.

If you’ve had any type of test or procedure with a radioactive substance seven days before the LH blood test, let your doctor know. These substances can interfere with the results of your test.

Your doctor can tell you when results of your test will be available and will discuss the meaning of your levels with you. According to the Department of Pathology and Laboratory Medicine at the University of California, San Francisco, the following values are normal LH blood levels measured in international units per liter (IU/L):

• women in the follicular phase of the menstrual cycle: 1.9 to 12.5 IU/L
• women at the peak of the menstrual cycle: 8.7 to 76.3 IU/L
• women in the luteal phase of the menstrual cycle: 0.5 to 16.9 IU/L
• pregnant women: less than 1.5 IU/L
• women past menopause: 15.9 to 54.0 IU/L
• women using contraceptives: 0.7 to 5.6 IU/L
• men between the ages of 20 and 70: 0.7 to 7.9 IU/L
• men over 70: 3.1 to 34.0 IU/L

While each result can vary based on your unique condition, some general interpretations of LH results can include the following.

For women

If you’re a woman, increased levels of LH and FSH can indicate a problem with your ovaries. This is known as primary ovarian failure. Some causes of primary ovarian failure can include:

• ovaries that are not properly developed
• genetic abnormalities, such as Turner syndrome
• exposure to radiation
• history of taking chemotherapy drugs
• autoimmune disorders
• ovarian tumor
• thyroid or adrenal disease
• polycystic ovary syndrome (PCOS)

Low levels of both LH and FSH can indicate secondary ovarian failure. This means another part of your body causes ovarian failure. In many cases, this is the result of problems with the areas of your brain that make hormones, such as the pituitary gland.

For men

If you’re a man, high LH levels can indicate primary testicular failure. The causes of this condition can include:

• chromosome abnormalities, such as Klinefelter syndrome
• gonad development failure
• a history of viral infections, such as the mumps
• trauma
• radiation exposure
• history of taking chemotherapy medications
• autoimmune disorders
• tumors, such as a germ cell tumor

Secondary testicular failure can also be due to a brain-related cause, such as a disorder in the hypothalamus. Also, if your doctor has given you the GnRH shot and your LH levels went down or stayed the same, a pituitary disease is often to blame.

Low levels of LH in adult males may lead to low testosterone levels, potentially causing such symptoms as:

• sexual dysfunction
• lack of sexual interest
• fatigue

For children

For children, high levels of LH can cause early puberty. This is known as precocious puberty. According to the American Association of Clinical Chemistry (AACC), girls are more likely to experience this condition than boys. Underlying causes of this can include:

• a tumor in the central nervous system
• trauma or brain injury
• inflammation or infection in the central nervous system, such as meningitis or encephalitis
• a history of brain surgery
• a history of irradiation to the brain

Delayed puberty with normal or lower LH levels can indicate underlying disorders, including:

• ovarian or testicular failure
• hormone deficiency
• Turner syndrome
• Klinefelter syndrome
• chronic infection
• cancer
• an eating disorder

Medications that can change LH levels include:

• anticonvulsants
• clomiphene
• digoxin
• hormone treatments
• birth control pills

Testing LH has the potential to indicate a number of development- and fertility-related disorders. If your doctor suspects you may have a condition that affects the ovaries, testicles, or the parts of the brain that make LH, the test can provide more information.