Hair loss blood test: which values should you check?

The question we get most about hair loss is not whether it passes. It is: which values should I have measured?

Honest answer: with a receding hairline and nothing else, usually none. With hair thinning everywhere at once, it is a different story.

Below I walk through every value in such a panel, with a column you will not see elsewhere. Namely when a value gets you nothing.

Which blood values belong in a hair loss panel?

In practice it comes down to six measurements: ferritin, haemoglobin, TSH, free T4, vitamin D and vitamin B12. Zinc is sometimes added. Together they cover the conditions that can help explain diffuse shedding and that you can actually act on. They say nothing about hereditary baldness itself.

That right-hand column is the point of this article. A lab that sells you everything measurable is doing you no favours.

What does ferritin say about hair loss?

Ferritin shows how much iron you hold in reserve, and that reserve runs down before your haemoglobin falls. So ferritin can be low while your blood count still looks normal. In diffuse hair shedding this is the value most doctors look at first.

Even so the evidence is less hard than supplement pages suggest.

A review in the Journal of the American Academy of Dermatology found insufficient grounds to screen everyone with hair loss for iron deficiency as standard (Trost, 2006). The authors describe the link between iron and the various forms of hair loss as inconsistently reported.

There is something more important, and it is not about your hair.

Men do not lose blood monthly. A low ferritin in a man is therefore never only a dietary matter, and belongs in a conversation with your GP. The Dutch NHG guideline on anaemia describes which causes then come into view.

More on that is in iron deficiency in men, and we explain the ferritin value itself on our page about ferritin.

Do you need to fast for a hair loss blood test?

For ferritin, TSH, vitamin D and B12 you do not need to fast. There is a preparation that matters far more and that almost nobody mentions: stop high-dose biotin at least 48 hours beforehand. It sits in nearly every hair supplement and can distort your results.

This is not a theoretical risk.

Many laboratory assays use biotin in the measuring reaction. In a JAMA study, healthy adults took 10 mg of biotin a day, described by the researchers as a dose common in over-the-counter supplements, after which several hormone assays went off (Li, 2017).

The advice to stop at least 48 hours before the draw comes from the same field (Luong, 2019).

The bitter joke: men with hair loss are exactly the ones taking hair vitamins, and exactly the ones having their thyroid measured. That is the wrong combination on the wrong day.

When does testing for hair loss make no sense?

If your hairline has been receding gradually for years at the temples and crown, and you have no other complaints, blood testing rarely turns anything up. That pattern fits hereditary hair loss, and there is no blood value for it. With round bald patches or a red, flaking scalp, your GP is the right first step too.

Thuisarts describes in plain language when to see your GP about hair loss.

What men often still want to know: what about my testosterone? Understandable question, and still the wrong turn. Baldness is about how sensitive your follicles are to DHT, not about how high your testosterone runs.

If you also have low energy, less interest in sex or difficult muscle gain, testing does make sense. You are then testing those complaints. That story is in low testosterone in men.

The whole pattern story, including when testing does help, is in hair loss in men.

What do you do with a normal result?

A normal result is not a wasted test. You have crossed off iron deficiency and a thyroid problem, and that saves you months of looking in the wrong direction. With diffuse loss and normal values, the cause more often lies in an event one to three months ago.

Imagine two men who both have a ferritin of 30 micrograms per litre.

The first has watched his hairline recede slowly for six years and feels fine otherwise. For him that 30 changes little, because his pattern points to inherited tendency.

The second has been losing hair everywhere for two months and is exhausted. For him the very same 30 is worth raising with his GP.

Same number, two different conversations. Without the pattern alongside it, a single value says little.

Think of surgery, a high fever, sharp weight loss or a new medication.

That form usually recovers on its own. Count on six months to a year.

If your thyroid does come back abnormal, read hair loss and your thyroid. If you are considering a treatment, we compare them in minoxidil experiences.

What you can do now

Look at the pattern first and only then at a tube of blood. Diffuse loss plus complaints is a good reason to test, a slowly receding hairline is not.

If you take hair vitamins, put them away two days before the draw. Otherwise you are paying for a result you cannot trust.

If you want ferritin, TSH, free T4, vitamin D and B12 measured in one go, they sit together in our extended health checkup. If you only care about your iron stores, the iron status test is enough.

Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.

References

1. Trost LB, Bergfeld WF, Calogeras E. The diagnosis and treatment of iron deficiency and its potential relationship to hair loss. J Am Acad Dermatol. 2006. PMID 16635664.
2. Almohanna HM, Ahmed AA, Tsatalis JP, Tosti A. The role of vitamins and minerals in hair loss: a review. Dermatol Ther (Heidelb). 2019. PMID 30547302.
3. Li D, Radulescu A, Shrestha RT, et al. Association of biotin ingestion with performance of hormone and nonhormone assays in healthy adults. JAMA. 2017. PMID 28973622.
4. Luong JHT, Male KB, Glennon JD. Biotin interference in immunoassays based on biotin-strept(avidin) chemistry: an emerging threat. Biotechnol Adv. 2019. PMID 30872068.
5. Favresse J, Burlacu MC, Maiter D, Gruson D. Interferences with thyroid function immunoassays: clinical implications and detection algorithm. Endocr Rev. 2018. PMID 29982406.