An FSH and LH test is a simple blood draw that measures two hormones produced by your pituitary gland: follicle-stimulating hormone (FSH) and luteinizing hormone (LH). These hormones control your reproductive system, and their levels can reveal why you’re experiencing fertility problems, irregular periods, early puberty, or symptoms of menopause. The test is one of the first steps doctors use to evaluate reproductive health in both women and men.
What FSH and LH Do in Your Body
Both hormones are made by a small gland at the base of your brain called the pituitary. They travel through your bloodstream to the ovaries or testicles, where they direct the production of eggs, sperm, and sex hormones like estrogen and testosterone. The two work as a team, but each has a distinct job.
In women, FSH drives the growth and maturation of egg-containing follicles in the ovaries during the first half of the menstrual cycle. LH then surges mid-cycle to trigger ovulation, releasing the mature egg. After ovulation, LH helps maintain the structure left behind (the corpus luteum), which produces progesterone to support a potential pregnancy.
In men, LH signals cells in the testicles to produce testosterone. FSH acts on a different set of cells, called Sertoli cells, that nurture developing sperm. Testosterone is considered the master switch for sperm production, but FSH determines the quality and quantity of sperm. Together, they keep the process running.
Why Your Doctor Orders This Test
Doctors order FSH and LH testing for a wide range of reproductive concerns. The most common reasons include:
- Irregular or absent periods. When periods stop or become unpredictable, FSH and LH levels help pinpoint whether the problem is in the ovaries, the pituitary gland, or the hypothalamus (the brain region that controls the pituitary).
- Difficulty getting pregnant. The test can show whether you’re ovulating normally and whether your ovarian reserve is declining.
- Suspected menopause or perimenopause. Rising FSH is one of the hallmarks of the transition into menopause.
- Low testosterone in men. FSH and LH help distinguish whether low testosterone comes from a testicular problem or a pituitary problem.
- Low sperm count. In men with small, firm testicles and very low or absent sperm counts, elevated FSH can point to a chromosomal condition like Klinefelter syndrome rather than a pituitary issue. If testicular size is normal, FSH helps determine whether the cause is impaired sperm production or a physical blockage.
- Early puberty in children. High FSH and LH in a child developing sexually before age 8 (girls) or 9 (boys) confirms precocious puberty.
How the Test Works
The test requires a standard blood draw, typically from a vein in your arm. For women who are still menstruating, timing matters. FSH and LH levels shift dramatically across the menstrual cycle, so most doctors request the sample on day 2 or 3 of your period (the early follicular phase), when baseline levels are most stable and easiest to interpret. If you’re being tested for menopause or if you haven’t had a period in months, timing is less of a concern.
Hormonal medications can affect your results. Birth control pills, hormone replacement therapy, and other hormonal treatments suppress or alter your natural FSH and LH levels, so your doctor may ask you to stop these before testing. Results usually come back within a day or two.
Normal Reference Ranges
FSH and LH levels are reported in international units per liter (IU/L). What counts as “normal” depends on your sex, age, and where you are in your menstrual cycle.
Women
During the follicular phase (the first half of your cycle), both FSH and LH typically fall between 1 and 12 IU/L, with FSH between 1 and 9 IU/L. At ovulation, LH surges to somewhere between 16 and 104 IU/L, and FSH rises to 6 to 26 IU/L. During the luteal phase (after ovulation), both hormones drop back down to early-cycle levels. After menopause, FSH climbs significantly and stays elevated.
Men
Adult men have relatively stable levels. At around age 30, typical ranges are roughly 1.9 to 9.7 IU/L for LH and 1.5 to 10.3 IU/L for FSH. These shift slightly upward with age. By 70, the FSH reference range is approximately 2.7 to 14.2 IU/L.
Labs may report slightly different ranges depending on the equipment they use, so always compare your numbers to the specific reference range printed on your results.
What High Levels Mean
When your ovaries or testicles aren’t producing enough sex hormones, the pituitary gland responds by pumping out more FSH and LH, trying to force them to work harder. So high levels usually point to a problem in the reproductive glands themselves rather than in the brain.
In women, elevated FSH can signal primary ovarian insufficiency (when the ovaries stop functioning normally before age 40), perimenopause, menopause, or a chromosomal condition like Turner syndrome. An FSH level above 30 IU/L, combined with at least a year without periods, is generally accepted as confirmation of menopause. Women with elevated but not fully postmenopausal FSH levels can still become pregnant, so contraception remains important during the transition.
In men, high FSH often indicates damage to or a problem with the testicles. Possible causes include Klinefelter syndrome, a history of mumps that affected the testicles, physical injury, or germ cell tumors. In both sexes, autoimmune diseases, radiation therapy, and chemotherapy can damage reproductive glands and push FSH levels up.
What Low Levels Mean
Low FSH and LH suggest the pituitary gland or hypothalamus isn’t sending the right signals. This condition, called hypogonadotropic hypogonadism, means the reproductive system is underperforming not because the ovaries or testicles are broken, but because they aren’t receiving instructions.
In women, low levels combined with absent periods typically point to a pituitary or hypothalamic cause. In men, low FSH and LH alongside low testosterone suggest the same. A pituitary tumor is one of the more common causes. As it grows, it can compress surrounding tissue and reduce hormone output. Other causes include severe blood loss during childbirth (Sheehan syndrome), brain infections like meningitis, inflammation of the pituitary from an immune reaction, stroke or bleeding in the brain, and certain medications including high-dose steroids and narcotics. In rare cases, a genetic mutation passed down in families is responsible.
FSH and LH Together: The Ratio Matters
Doctors often look at the relationship between FSH and LH, not just the individual numbers. In a normal menstrual cycle, FSH is slightly higher than LH during the follicular phase. When LH is disproportionately high compared to FSH, it can raise suspicion for polycystic ovary syndrome (PCOS), though the LH-to-FSH ratio alone isn’t enough to diagnose the condition. Current guidelines use LH testing mainly to assess whether ovulation is occurring in women with uncertain menstrual histories, rather than relying on the ratio as a standalone diagnostic tool.
This is why your doctor may also order additional tests alongside FSH and LH, such as estrogen, testosterone, thyroid hormones, or imaging, to build a complete picture before making a diagnosis.
Repeat Testing and What Comes Next
A single set of FSH and LH results doesn’t always tell the full story. Because these hormones fluctuate naturally, your doctor may repeat the test at two- to three-month intervals to see whether levels are trending in a particular direction. This is especially useful during perimenopause, when FSH can bounce between normal and elevated for months or even years before settling into a consistently high range.
If results come back abnormal, the next steps depend on what the numbers suggest. High levels pointing to ovarian or testicular failure may lead to imaging, chromosomal testing, or a referral to a reproductive endocrinologist. Low levels suggesting a pituitary problem often prompt an MRI of the brain to check for tumors or structural issues. For fertility concerns, the results help guide decisions about treatment options and timing.