Hormone blood tests: what they can and cannot tell you

A hormone blood test can help answer a specific medical question, but it cannot give you a complete fertility forecast. Your clinician needs to consider the results alongside your symptoms, age, medical history and, sometimes, other tests.

What the tests look for

FSH stands for follicle-stimulating hormone. It helps eggs develop in the ovaries and prepares them for ovulation. Testing can help investigate periods that have become irregular or stopped, as well as some fertility problems. Your clinician will consider why the test was requested when explaining the result.

LH, or luteinising hormone, helps trigger egg release. FSH and LH both come from the pituitary gland. An LH blood test may be part of an investigation; it is different from a home ovulation test, which measures LH in urine.

Oestradiol is often assessed alongside FSH. In people whose periods have stopped, the combined results can help a clinician investigate how the ovaries and hormone signals are working. Progesterone testing can help assess whether ovulation has recently happened when the sample is taken at an appropriate time.

TSH means thyroid-stimulating hormone. It can help identify thyroid disorders as part of investigating disrupted ovulation. Prolactin is a pituitary hormone whose main roles include breast development during pregnancy and milk production afterwards. Raised prolactin can also affect ovarian function and periods.

You may not need all these tests. ASRM does not recommend prolactin as a routine part of every infertility assessment, for example; it can be appropriate with milk-like nipple discharge or infrequent or absent periods. Ask what each requested test is meant to find out.

Timing can change what a result tells you

Hormone levels change through the cycle. A clinician may request FSH and oestradiol early in the follicular phase, while progesterone is usually checked later. ASRM recommends timing progesterone approximately 1 week before the expected next period, rather than assuming the same cycle day suits everyone.

If your periods are unpredictable, ask the clinician who requested the test how to arrange the sample. Give the first day of the last period if you know it, and say when you are estimating. A single progesterone measurement may support evidence of ovulation, but it cannot assess the quality of the luteal phase.

Tell the clinician about medicines and supplements before testing. Follow their preparation instructions, and do not stop a prescribed medicine without talking to your doctor. Ask who will explain the results and whether you might need another sample.

AMH is not a fertility expiry date

Anti-Müllerian hormone, or AMH, is made in ovarian follicles. It helps assess ovarian reserve, the supply of eggs, and can help plan fertility treatment. It does not measure egg quality or predict whether you will become pregnant.

A home AMH test measures the same hormone, so buying it privately does not remove those limits. ASRM cautions against using ovarian-reserve testing as a random marker of ovarian function in people without infertility. A result on its own cannot tell you that you can safely delay trying for pregnancy, or that pregnancy is impossible.

Why perimenopause often needs no blood test

NICE advises identifying perimenopause without laboratory tests in otherwise healthy people aged 45 or over who have newly started hot flushes or sweats and menstrual changes. MedlinePlus similarly says FSH testing usually is not needed at age 45 or older. Symptoms and context can provide the information needed; a blood test is not a requirement for discussing care.

Hormonal treatments can make assessment more complicated. NICE sets limits on using FSH tests with combined hormonal contraception. It also sets separate limits on how its guidance applies to people using gender-affirming hormone therapy. Tell the clinician which treatments you use, rather than applying the usual age-based advice to yourself.

When to arrange a review

Book a GP appointment in the UK, or see your doctor in the US and elsewhere, if periods become irregular or you miss your period 3 times in a row. Ask the clinician who ordered a test to explain what question it answered, what remains uncertain and what happens next. Bring privately obtained results to that conversation too.