What a Hormone Blood Test Can Tell You, and What It Can't

Week 1 of my 90 days did not go the way I planned it. Shifts back to back, a pile of paperwork with a date on it, and by Thursday the wake time I'd promised myself had turned into whatever time I stopped. I got the daylight twice. Twice out of seven.

I'm telling you that because of what I did at the end of the week instead of quietly deciding to start again in October. I booked my own bloods.

Not because a blood test fixes a bad week. Because I'd rather know where I'm starting from than guess at it, and because the question I'm asked more than any other is some version of the same thing: can't we just test my hormones and find out what's wrong with me?

The honest answer is longer than yes or no. So here it is, including the part most people don't expect.

The test everybody asks for, and what it actually does

The one women ask for by name is FSH, follicle stimulating hormone. It's the hormone your brain sends to your ovaries, and it climbs as the ovaries become harder to persuade. So it sounds like the perfect test for perimenopause.

It isn't, and the national guidance says so plainly. NICE guideline NG23 on menopause, updated in November 2024, is that in women aged 45 and over with typical symptoms, perimenopause is a clinical diagnosis. FSH isn't required, and a normal FSH doesn't rule it out.

The reason is in the biology. In perimenopause FSH doesn't rise in a tidy line, it swings. Test on a Tuesday and it's normal. Test the same woman 3 weeks later, with the same symptoms and the same disrupted sleep, and it's raised. One number from one morning tells you about that morning.

That matters because of what gets done with a normal result. A woman is told her hormones are fine, she goes home, and the thing she came in about is still happening. The test didn't say she was fine. It said her FSH was normal that day, which was never the question.

FSH does earn its place in 2 situations. Under 45, where the picture is genuinely uncertain and the answer changes what you'd do. And under 40, where it isn't optional: premature ovarian insufficiency affects around 1 in 100 women under 40, it's diagnosed on FSH above 25 on 2 readings taken 4 to 6 weeks apart, and it needs treating differently and sooner, because it's about bone and heart health for decades, not just symptom relief.

So what are the bloods actually for?

Not for finding perimenopause. For ruling out the things that look exactly like it, and for seeing what else is going on while we're already looking.

That's the part that gets skipped, and it's the part that changes plans.

Thyroid. TSH, free T4, free T3, and thyroid antibodies once in a lifetime. An underactive thyroid mimics perimenopause almost perfectly: tired, cold, heavy periods, flat mood, weight that won't shift, hair thinning. It's common in women, it's very treatable, and it gets missed for years because the symptoms are the ones everybody expects at 45.

Iron, properly. Not just haemoglobin. Ferritin, iron, transferrin saturation, the whole picture. Iron deficiency is extremely common in women in their 40s, particularly with heavy periods, and you can be deficient with a completely normal full blood count. It causes the exact fatigue and brain fog that women are told is "just your hormones". If you've ever been told your bloods were normal and you still can't get through the afternoon, this is the number I'd want to see.

B12 and vitamin D. Both common, both fixable, both perfectly capable of producing fatigue and low mood on their own.

HbA1c, lipids, and SHBG. Insulin sensitivity and cholesterol both shift across the menopause transition, and they shift quietly. SHBG is the quiet one worth knowing about: a low result is one of the earliest useful signals of insulin resistance in a woman, years before anything shows up elsewhere. These are a starting point, not a verdict.

Prolactin. Raised prolactin has its own causes and its own treatment, and it's worth excluding before a changed cycle gets filed under perimenopause and left there.

Put together, that's the difference between "your hormones are normal" and knowing which of 5 possible explanations is actually yours.

Where the blood comes from, and why that's changed

The old obstacle was never the test. It was the logistics: a morning off, a drive, a waiting room, a car park, and a phone call 3 weeks later that you missed.

From this week there are 2 routes at my clinic, and both of them happen at your house.

A self-taken kit, posted to you. It's a small device that sits on your upper arm and collects the sample without a needle in a vein. Warm hands, a few minutes at your kitchen table, and back in the prepaid envelope. Most of the panel runs perfectly well on a sample collected this way.

A nurse comes to you. Booked at a time that suits you, at your address, and taken from the arm in the usual way.

They're not interchangeable for everyone, which is why the choice is made at the consultation rather than on a website. A full blood count only runs on a venous sample, and anyone on testosterone or starting it needs the venous route, because haematocrit has to be monitored properly. For most women asking the ordinary question, the kit is enough.

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What sometimes follows a result, if you want it

Any pharmacy equivalent at the same amounts does the same job, and some sachet sizes run thin here, so the capsules are the reliable option. Iron is the one to be careful with: taken without a reason it can do harm rather than nothing, and iron is a leading cause of accidental poisoning in young children, so it belongs out of sight and reach. Food supplements are not intended to diagnose, treat, cure or prevent any condition.

How to prepare, so the result means something

A badly timed sample is worse than no sample, because it gets acted on. 4 things make most of the difference.

Go in the morning. Iron and several hormones are highest early and drift through the day. Consistency matters more than perfection, so if you retest later, retest at the same sort of time.

Write down your cycle day. Count from the first day of your last proper bleed, and put the number on the form. Progesterone in particular means almost nothing without it, and a result read against the wrong day is how women get told something is wrong when it isn't.

Stop biotin 2 to 3 days before. This one catches people out constantly. Biotin is in most hair, skin and nail supplements, often at very high doses, and it interferes with the way many labs run thyroid tests. It can push a result in either direction, which means it can invent a thyroid problem or hide a real one. Stopping it for a few days costs you nothing.

Water yes, coffee no. Drink water normally, and be well hydrated, because a dehydrated sample is a harder sample to take and a harder one to read. Whether you need to fast depends on which panel you're having, and you'll be told which before the kit arrives.

And then what happens

This is the bit that decides whether the whole thing was worth doing.

Results get read with you, not emailed at you with a green tick and a leaflet. We go through what each number means for you specifically, against the symptoms you came in with and against your family history, which is the most under-asked question in women's health and the one I'd most like you to go and ask your mother about while you still can.

Then there's a plan, and it's ordered rather than piled up: the thing most likely to move first, the thing that waits, and the thing we retest in 3 months to see whether any of it worked. Where that plan needs a treatment, I work with an independent pharmacy that supplies what's been chosen at the consultation, so you're not sent off to start the conversation again somewhere else.

And where something sits outside what I should be handling, I say so, and I write the letter the same day rather than handing you back the problem.

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Anyone taking a blood thinner should check vitamin K2 with a pharmacist before starting it. Food supplements are not intended to diagnose, treat, cure or prevent any condition.

Where I've got to

My own bloods are booked, on the same terms as anybody else's, and I'll tell you what comes back and what I do about it, because I said at the start of these 90 days that I should be able to say I've tried something before I recommend it.

And Week 2 starts tomorrow regardless of how Week 1 went, because that's the whole point of building it as a chain rather than a reset. You don't go back to zero. You pick up the link you dropped, and mine is the wind-down, not the wake time.

If you want your own numbers looked at rather than the general version, the door is the Women's Health Consultation, and the tests get arranged out of that conversation once we know which ones are actually worth doing for you.

I write to my list every Sunday morning, one thing worth knowing and what I'm doing about it myself. Beyond Prescriptions is here.

Debora Tentis, Women's Health Pharmacist.