Which Blood Tests to Ask For When Your Hair Is Shedding
Ask for three blood tests: ferritin, thyroid (TSH with free T4) and vitamin D. If the scalp itself looks different, with patches, itching, redness or pain, the route changes: you need a doctor who looks at skin, and no blood draw replaces the look. Below: the sentence to say at the appointment, why "your bloods are normal" so often means the right test was never run, and what to tell the doctor before the tests are chosen.
Ask for these by name
At your next appointment, say: "I would like my ferritin and thyroid checked, not just a full blood count." A full blood count is the standard tube. Ferritin and a thyroid panel are separate tests, and they are not in it unless someone adds them.
Write each result down with its date and the lab's lower limit, the limit printed next to your number on the report. You will need both later, and nobody will write them down for you.
Tell the lab or the doctor if you take biotin, the vitamin sold for hair and nails. It can distort some blood tests, thyroid tests among them. Say it out loud and ask the doctor how to handle it. Do not decide that part alone.
Say too if you have taken iron tablets recently. They can lift the ferritin result and make your stores look better than they are.
Find your case
| Your number | What it means | What to ask for | First step |
|---|---|---|---|
| Full blood count came back normal | It shows the iron in circulation, carried by red cells. It does not show how much iron is stored. | Ferritin, by name, added to the request | Write down the result, the date and the lab's lower limit |
| Ferritin: you were never told, or it was never run | Ferritin is the iron your body keeps in storage. Low stores are a pattern linked with shedding. | The actual result and where it sits against the lab's lower limit | Ask what the doctor makes of it for you, and what would confirm or rule out iron as a cause |
| Tired, cold, shedding, and no thyroid test on file | TSH is the signal your brain sends to the thyroid. Free T4 is the thyroid hormone itself, available to your tissues. | TSH and free T4, drawn together | If TSH looks borderline and symptoms are many, ask about thyroid antibodies |
| Iron and thyroid are covered, shedding goes on | Vitamin D is the third request, after the first two are done. | Vitamin D, added to the same blood draw | Write the result down with the date, like the others |
| Scalp looks different: patches, itching, redness, pain, hairs breaking at the root | The cause sits in the skin or the hair shaft, and blood tests answer little about it. | A referral to a dermatologist, the doctor who looks at skin | Photograph the area, with the date, before the appointment |
Why a normal blood count does not rule out low iron
A full blood count measures the iron in circulation, the iron carried around by red cells right now. Ferritin measures the storeroom. The body protects the blood by spending from the storeroom, so stores can run low while the count still reads normal.
That is the usual reason "your bloods are fine" and "your hair is falling out" sit in the same appointment. Ten minutes is not much time. The standard set gets ordered, and ferritin is often not in it. Nobody looked in the storeroom.
The word "normal" is a second trap. A lab's normal band is built from a general population. It marks where the lab stops worrying, which may sit far from where you feel well. That is why you write down your number and the lab's lower limit. A result just above the line can be read in more than one way, and the doctor may read it differently when you ask the question directly.
If ferritin is low, the next question is why. Heavy periods, a diet low in iron, trouble absorbing it from food and recent blood loss are the usual places to look. Raise them in the same appointment.
What to ask about your thyroid
Ask for TSH, the signal your brain sends to the thyroid, and free T4, the thyroid hormone itself, the part free to act on your body. TSH on its own can miss part of the picture, so ask for the two together.
TSH can land at the edge of the normal band and leave you with a long list of symptoms. Then ask a second question: "Should my thyroid antibodies be tested?" Antibodies are proteins that show the body is attacking its own tissue by mistake. They are a separate blood test, and they are often not run unless someone asks.
Two pages on this site go through that situation in detail: Mildly Raised TSH: Does It Go Away on Its Own? and Hashimoto's With a Normal TSH: Can It Still Cause Symptoms?. Read them before the appointment if your result sits near the edge.
The tests cannot tell you the thyroid is the cause. They show whether it is a candidate. The doctor decides what the pattern means.
Why vitamin D comes third
The link between vitamin D and hair shedding is less well studied than the link with iron or the thyroid. That is the one real gap in this list, and the reason to ask for iron and thyroid first.
There is still a practical case for adding it. It is a simple test, it goes on the same blood draw, and the result gives you one more thing to write down and discuss. If it comes back low, that is a conversation with the doctor, not a verdict on your hair.
Do not buy a supplement before the result is back. The result is the reason to discuss one, and the dose is the doctor's decision.
What to tell the doctor before they pick the tests
Shedding usually shows up long after its cause. A hair that falls today was set on its way out earlier, so the trigger is often something you have stopped thinking about.
Before the appointment, go back through the time before the shedding began and write down what you find:
An illness, even one you recovered from. A birth. Sudden weight loss, or a stretch of eating very little. A change of tablets, including contraceptives, started or stopped. A period of severe stress. Heavy periods, if they are your normal.
Hand the doctor that list. It narrows the search and can change which tests make sense. Add what you take every day, including biotin and any recent iron tablets, since both can change how a result reads.
If your periods have also shifted, say so in the same breath. Cycle changes and shedding together point to a different set of tests, covered in Can a Blood Test Show Perimenopause? It Depends on Your Age.
The list will not prove a cause, and sometimes no cause is found. It still gives a ten-minute appointment something to work with.
When the problem is the scalp, not the blood
Some hair problems start in the skin, and blood work says little about them. Book a dermatologist, the doctor who looks at skin, if you see any of these:
Bare patches with no hair at all. Itching or burning. Redness or flaking. A scalp that is sore to touch. Hairs that snap off at the root instead of falling out whole.
Take dated photographs, and tell the doctor what you have already had tested. Ask whether a closer look at the scalp is needed. The skin appointment sits beside the blood tests above and does not replace them.
If the blood work comes back and the scalp still looks different, the next step is the skin. Arrive with your results and photographs in hand.
What to do with this
- Say "ferritin and thyroid" by name, because a full blood count includes neither
- Write down every result with its date and the lab's lower limit
- Tell the lab and the doctor about biotin and recent iron tablets before the draw
- Go back over what happened before the shedding began and hand the doctor that list
- See a dermatologist when the scalp has patches, itching, redness or pain
Questions people also ask
Can hair shed when my blood count is normal?
Yes. A full blood count shows the iron in circulation. Ferritin shows the stored iron, and it is a separate test. The body protects the blood by spending from stores, so the count can look fine while the stores run low. Ask for ferritin by name.
Should I see a dermatologist first or have blood tests first?
If the scalp has patches, itching, redness, pain or hairs breaking at the root, see a dermatologist. If hair is thinning evenly and the scalp looks ordinary, start with the blood tests. You can do both, and each makes the other appointment more useful.
Does biotin matter before a thyroid test?
Biotin can distort some blood tests, thyroid tests among them. Tell the lab and your doctor you take it and ask how to handle it. Do not decide on your own. The doctor knows how your lab runs the test.
This article is information, not medical advice, diagnosis or treatment. Reference ranges, doses and protocols differ between people and between laboratories. Talk to a qualified clinician before changing anything about your care.