Hair and iron markers
Telogen Effluvium Blood Tests: What to Ask For
Reviewed by a qualified clinician · analysed at UKAS-accredited UK labs (ISO 15189)
Last reviewed September 20265 min read
Every Helvy guide is written by our health editors, then checked by a qualified clinician before it goes live and re-checked as the science moves. We name clinical roles, not individuals, until each reviewer has agreed to be credited publicly. This is wellness guidance to help you understand your own data, not a diagnosis.
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No blood test diagnoses telogen effluvium. The British Association of Dermatologists says a blood test is used to rule out other causes, naming thyroid conditions and iron deficiency. So the markers to ask for are ferritin, a full iron panel and thyroid function.
Not sure which markers you need? Build your test →The hair in the shower drain stopped being normal weeks ago. It is coming out from everywhere, not in patches, and it started for no reason you can see.
There probably is a reason. It just happened a while back, and that gap is the most useful thing to understand here.
1. What is telogen effluvium?
Too many hairs entering their resting phase at once, then falling out together.
Your hair does not grow continuously. Each follicle cycles between growing and resting, and the resting phase is called telogen. The BAD leaflet puts numbers on it. Normally about 15 per cent of scalp hair is shedding. In telogen effluvium that rises to 30 per cent or more.
The shedding comes from all over the scalp rather than in patches. That pattern is part of how it is told apart from other kinds of hair loss, which our hair loss blood test guide covers more broadly.
2. Why did it start for no reason?
Because the trigger was months ago. The BAD leaflet says shedding “can occur around 3 months after a trigger”.
So think back a season, not a week. A bad illness, surgery, a crash diet, childbirth, a period of real stress, a new medicine. The hair was committed to its resting phase then, and it is only leaving now.
The same leaflet says the shedding phase lasts between three and six months, and that anything beyond six months is considered chronic. That timeline is worth knowing before you panic.
3. What is a blood test actually for here?
Ruling other things out. Diagnosis is made by looking at the scalp and taking a history, not by a lab result.
“A blood test may be carried out to exclude other possible causes of hair loss. These causes can include thyroid conditions and iron deficiency.”
Two named causes, from the dermatologists themselves. That is your shopping list, and it is shorter than the internet suggests.
4. Which markers should you ask for?
Four, and they follow directly from that quote.
- Ferritin. The protein that holds iron in reserve, so it shows how much iron you have banked.
- A full iron panel. Serum iron, transferrin and transferrin saturation say whether iron is moving, not just stored.
- TSH. The pituitary signal that goes up when the thyroid is underperforming.
- Free T4. The thyroid hormone itself, which places a borderline TSH.
Our thyroid blood test guide explains that pairing, and the iron deficiency guide covers the iron set.
5. Why is ferritin the one people argue about?
Because a ferritin can be inside the lab range and still be low for hair.
The printed floor in most UK labs sits near 15 to 30 depending on the lab, which is the level below which iron stores are considered empty. Dermatology practice often works to a higher figure when shedding is the problem, and that difference is where most frustrating conversations start.
The leaflet also makes the practical point. It says telogen effluvium “can reoccur if the possible underlying cause such as iron deficiency is not treated”. So the number matters beyond this episode.
Our guide to optimal ferritin levels sets out where those thresholds come from, and ferritin levels by age shows how the usual reading shifts.
6. What should you do next?
Write down two things before you see anyone.
- The date it started. Then count back three months and write down what was happening then.
- Your actual numbers. Ask for the ferritin and TSH values, not just the word normal.
See a GP rather than waiting if the hair is coming out in patches, if the scalp is sore or scaly, or if shedding has run past six months. Those are different problems with different answers.
A blood test measures the marker. Only a qualified clinician can put it beside your history and say what it means for you.
7. Which blood test reports these markers?
Helvy’s Vitamins & Minerals panel (£159) reports ferritin with serum iron, transferrin, transferrin saturation and TIBC, plus vitamin D, B12, folate and magnesium. Our Thyroid & Vital Organs panel (£159) reports TSH with free T4 and free T3.
Two honest limits. No panel of ours contains both sets, so pick the question you most want answered first. And neither is an anaemia screen, which also needs a full blood count and a clinical judgement.
Not sure which fits? The build-my-test tool walks you through it, and the energy and fatigue hub collects our iron and thyroid guides.
READY TO TEST?
See ferritin in the company it keeps
Helvy’s home blood tests report the full iron workup together, so one ferritin does not have to carry the story alone. Samples are processed by UKAS-accredited UK labs.
Frequently asked questions
What blood tests are done for telogen effluvium?
The British Association of Dermatologists says a blood test may be done to exclude other causes, and names thyroid conditions and iron deficiency. In practice that means ferritin, the iron markers and thyroid function.
Can a blood test diagnose telogen effluvium?
No. The leaflet describes diagnosis as scalp appearance plus medical history, sometimes with a hair pull test. Blood markers are there to rule other causes in or out.
How long after a trigger does shedding start?
Around three months, according to the BAD leaflet. That delay is why the cause so often feels invisible, and why counting back a season is more useful than looking at last week.
How long does telogen effluvium last?
The shedding phase lasts between three and six months, after which new hair starts to grow. Returning to your usual volume can take many months longer.
What ferritin level is linked with hair shedding?
There is no single agreed figure. Lab ranges usually start somewhere between 15 and 30, and dermatology practice often works to a higher target where shedding is the problem, so ask for your actual number.
Can it come back?
The leaflet says it can recur if an underlying cause such as iron deficiency is not treated. That is the practical argument for knowing your ferritin rather than guessing.
Related guides
Hair Loss Blood Test UK
The wider set of markers behind hair thinning.
Ferritin Blood Test UK
What iron stores are and how they are measured.
Optimal Ferritin Levels UK
Where the higher targets come from, and why.
Thyroid Blood Test UK
TSH, free T4 and what they read together.
Iron Deficiency Blood Test
Ferritin, iron studies and what the results mean.
Perimenopause Hair Loss UK
When the timing points somewhere else entirely.
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