What an FSH test can tell you
"Can't they just do a blood test?" is one of the most common questions in this whole category, and the honest answer, per NICE guidance, is usually no — not because testing is difficult, but because the specific hormone involved fluctuates too much during perimenopause to make a single reading meaningful.
What NICE guidance actually says, by age
- 45 and over: FSH blood tests should not be used to identify perimenopause or menopause. Diagnosis is meant to be made on symptoms and menstrual history alone.
- 40 to 45: An FSH test can be considered to help confirm menopause, specifically alongside symptoms and a change in menstrual cycle — not as a standalone answer.
- Under 40: Testing should be considered where menopause is suspected, because this is the situation where a blood test result actually changes what happens next — investigating premature ovarian insufficiency, which is worth catching early. See when you are told you are too young for that specific situation.
Why a fluctuating hormone makes an unreliable single test
FSH concentrations vary considerably over short periods during perimenopause — a level that reads as "normal" one week can look completely different two weeks later, simply because of where you are in an increasingly erratic cycle. A single snapshot doesn't capture a moving pattern, which is exactly the problem with using it as a yes/no test at this stage. This is the specific, guideline-based reason a GP might decline to order one for someone over 45 — not a dismissal of the request, but a genuine limitation of the test itself.
What actually helps instead
Since blood tests are the wrong tool over 45, symptoms and menstrual history are what diagnosis is actually meant to be based on — which makes a dated symptom-and-cycle record the more useful thing to bring to that conversation than a request for a lab test. See tracking before your appointment and how periods change in perimenopause for what that record actually looks like.
This is general information about a published guideline, not medical advice. Whether a test is appropriate for you depends on your age and specific situation. HormoneLog does not perform, access, or interpret any blood test.
What NICE NG23 actually says. · How periods change in perimenopause. · When you are told you are too young.
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About HormoneLog
HormoneLog is an iOS app from Baker Ventures LLC for tracking perimenopause and menopause symptoms and keeping an HRT record: what you took, at what dose, from when, and what changed afterwards. It is built for the appointment, where "it has been bad lately" is worth far less than a dated record of frequency and severity. The app is in development.
HormoneLog is a record-keeping tool. It does not diagnose, does not score you, and makes no claim about symptom relief. The guides on this site link to NICE, the NHS, the Menopause Society and peer-reviewed sources, and say plainly where the evidence is thin. Everything here is free and needs no account.
Questions and answers
Can a blood test confirm I'm in perimenopause?
Usually no. NICE guidance is explicit that FSH (follicle-stimulating hormone) blood tests should not be used to identify perimenopause or menopause in people aged 45 or over, because levels fluctuate too much during this stage to be a reliable single reading.
When is an FSH test actually useful?
NICE guidance says it can be considered to confirm menopause in people aged 40 to 45 with symptoms, and it should be considered in people under 40 where premature ovarian insufficiency is suspected. Above 45, diagnosis is meant to be based on symptoms.
Why does a fluctuating hormone make a bad test?
A single blood draw catches one moment in a cycle where FSH can vary considerably from week to week during perimenopause. A normal-looking result on one day says very little about the pattern overall — it's the wrong kind of measurement for a fluctuating process.
Can HormoneLog do an FSH test or interpret one for me?
No. HormoneLog logs symptoms you report; it has no access to blood test results and doesn't interpret them. Whether a test is useful in your case, and what a result means, is a conversation with the person who ordered it.
HormoneLog. “What an FSH test can tell you.” Baker Ventures LLC, September 8, 2026. https://hormonelog.bakerventuresstudio.com/guides/what-an-fsh-test-can-and-cannot-tell-you/