The blood test everyone asks about
The hormone a test would usually measure is follicle-stimulating hormone, or FSH. The problem is that during perimenopause FSH swings widely from day to day, so a single reading can look normal one week and raised the next (Journal of Clinical Endocrinology & Metabolism, 2021). Because of that variability, measuring it is not recommended for women aged 45 and over with typical symptoms, and a normal result does not rule perimenopause out (NICE guideline NG23, 2024). The transition is recognised clinically, from the story your body is telling over months, rather than from a number on one morning.
How age changes the answer
Age is what decides whether any test is useful.
From 45 onward, symptoms that have recently started along with a change in your cycle are enough to recognise perimenopause, and no blood test is normally needed. Between 40 and 45, a doctor may sometimes use an FSH test to help make sense of symptoms, though it is still not required. Under 40, symptoms that suggest the menopause need proper assessment rather than being assumed, because a different pathway applies (NICE guideline NG23, 2024).
A doctor may also run tests for a different reason, to rule other things out. Very heavy or prolonged bleeding, a possible pregnancy, or symptoms that could point to something like a thyroid problem can all prompt tests that are about the cause, not about confirming perimenopause.
| Your age | What is usually recommended |
|---|---|
| 45 and over | No blood test needed; recognised from your symptoms and cycle change |
| 40 to 45 | A doctor may use an FSH test to help, though it is not required |
| Under 40 | Testing is used, because symptoms need fuller assessment |
A single FSH reading swings too much to be reliable, which is why age guides the approach.
What actually helps
The most useful thing is a clear record of your own pattern: how your cycle is changing, and which symptoms are turning up alongside it. That is what a doctor works from, and it is more informative than a one-off hormone level. Home menopause tests that measure FSH in urine share the same core limitation as the blood test, a single snapshot of a hormone that naturally jumps around.
When to talk to a doctor
See your doctor if symptoms start before 45, if your periods become very heavy or close together, if there is bleeding between periods or after sex, or if symptoms are affecting your daily life and you want to discuss options (NICE guideline NG23, 2024). anna does not diagnose, and this article is not medical advice.