FSH and LH Testing: A Guide to Fertility Hormones

What FSH and LH Do

Follicle-stimulating hormone, or FSH, and luteinizing hormone, or LH, are made by the pituitary gland. They are the main signals that drive the reproductive system. In women, they guide the growth of an egg each cycle and trigger ovulation. In men, they support sperm production and the making of testosterone.

The two hormones work as a team. FSH and LH tell the ovaries or testes to produce their own hormones, and those hormones in turn signal the pituitary to adjust FSH and LH. This back-and-forth keeps the system balanced. When one part changes, the others respond, and measuring the pair together often reveals more than either alone.

Both hormones are named for what they do. FSH helps a follicle mature in the ovary, while LH provides the trigger that releases the egg. Their names describe the process even when the tests are used to look at a broader concern.

How the pattern differs

In women, FSH and LH rise and fall in a predictable rhythm across the menstrual cycle, with a sharp surge of LH just before ovulation. Because of that rhythm, the meaning of a result depends on the day of the cycle. In men, the levels are steadier. A clinician interprets the numbers against the right reference range for sex, age, and cycle day.

The role of the pituitary

The pituitary sits below the brain and acts on signals from a region called the hypothalamus. If either control center is disturbed, FSH and LH can fall, and the ovaries or testes slow down. This is why these tests can point to a cause far from the reproductive organs themselves.

Why the Tests Are Ordered

• To explore difficulty conceiving
• To investigate irregular, absent, or very light periods
• To assess menopause or perimenopause
• To look into delayed or early puberty
• To evaluate low sex drive, low energy, or erectile problems in men
• To check pituitary function when other hormone problems are suspected

FSH, LH, and Ovarian Reserve

As the number of eggs in the ovaries declines with age, FSH tends to rise, because the pituitary must signal harder to prompt a response. For that reason, FSH is sometimes used as one clue about ovarian reserve, though it is not a precise measure of fertility on its own. Other markers, such as anti-mullerian hormone, are often used alongside it.

FSH and LH in Men

In men, FSH supports sperm production and LH drives testosterone. A high pair with low testosterone can point to a problem in the testes, while a low pair can point to the pituitary or brain. The pattern helps a clinician decide which direction to look next.

Puberty and the Hormone Signals

In children, FSH and LH help a clinician assess puberty that starts unusually early or late. The expected ranges change quickly with age during this period, so timing and age are central to reading the result.

Related Tests

FSH and LH are usually part of a group. A clinician may measure estradiol and progesterone in women, and testosterone in men, to see how the ovaries or testes respond. Thyroid and prolactin tests are also common, because an underactive thyroid or a high prolactin can disturb the reproductive signals. Anti-mullerian hormone and other fertility markers may be added when the question is ovarian reserve.

The surrounding tests matter because FSH and LH only show the signal. They do not show how the target organs are responding. Pairing them with the output hormones turns two numbers into a pattern.

How the Sample Is Collected

The test uses a standard blood draw from a vein, usually in the arm. For women, the clinician often chooses a specific day of the cycle, commonly early in the follicular phase, because the reference ranges depend on timing. Men can be tested on most days, and a morning sample is often used. Fasting is generally not needed. Tell the laboratory about hormone medicines or supplements, since these can change the results.

Getting the timing right

When a cycle is irregular, picking a day can be tricky. A clinician may use a hormone level or an ultrasound to judge where in the cycle a person is, so the FSH and LH values can be read against the right reference range.

Reading the Results

High FSH and LH with low sex hormones often suggest the ovaries or testes are not responding, so the pituitary signals harder. Low FSH and LH with low sex hormones can point to a pituitary or brain signal problem. A combination that fits neither pattern may need more testing. In women, a high FSH around menopause is expected, while a high FSH in a younger woman raises different questions.

No single value stands alone. The result is read with the person's age, cycle day, symptoms, and the other hormones in the panel. A mild abnormality is often repeated to confirm the pattern.

Why a Single Test Rarely Suffices

Because FSH and LH move with the cycle and with age, one value can be hard to place. A clinician often repeats the test or adds others before drawing a conclusion. The pattern across the panel usually matters more than any single number.

What Can Affect the Numbers

• Day of the menstrual cycle in women
• Age, which shifts the expected range
• Hormone medicines and supplements
• Pregnancy and breastfeeding
• Recent illness or severe stress
• Laboratory method, since ranges differ

Talking With Your Clinician

Bring the first day of your last period if you are a woman, because that detail fixes where in the cycle the sample was taken. List any hormone medicines or fertility treatments. These small facts often change how a result is read.

Putting It Together

FSH and LH tests help a clinician locate where a hormonal signal is going wrong. They are rarely diagnostic on their own, but paired with the right hormones and a clear history, they can point toward the next step. A specialist can explain what the pattern means for your situation.