Hair Loss Blood Test UK: Which Markers to Check, and What Your Results Actually Mean

1. Why a blood test is the first step for hair loss

Hair follicles are among the most metabolically active cells in the body. They divide rapidly, require a constant supply of iron, zinc, and amino acids, and are exquisitely sensitive to hormone fluctuations and nutrient depletion. Zinc is the one people reach for first, so it helps to know the daily zinc dose the NHS caps supplements at.

When the body is under metabolic stress, hair is one of the first systems to be deprioritised. That stress can come from iron deficiency, thyroid dysfunction, or high androgens. The body redirects resources to vital organs, and follicles shift from their growth phase (anagen) into a resting and shedding phase (telogen) prematurely.

A blood test identifies the underlying cause. Without one, you're guessing. Most over-the-counter hair supplements are expensive guesses. The British Association of Dermatologists lists blood tests as a standard investigation for anyone presenting with diffuse hair thinning.

2. Types of hair loss and their blood test clues

Not all hair loss is the same. Understanding the pattern helps determine which blood markers to prioritise.

Many people have overlapping causes. A comprehensive blood panel catches all of them in a single test. If you are a woman in your forties and your periods have changed too, the female pattern row is usually the place to start: see why hair thins in perimenopause for the hormone shift behind it. If the bleeding itself is heavy, the test your GP is told to run leaves ferritin out.

Which blood tests are done for telogen effluvium?

Telogen effluvium is the diffuse shedding that follows a shock to the body. An illness, a birth, surgery, a crash diet, a hard few months. Hair that would have kept growing drops into its resting phase all at once, then falls out about three months later. That delay is why the cause is usually already behind you by the time you notice.

The British Association of Dermatologists keeps the testing short:

“A blood test may be carried out to exclude other possible causes of hair loss. These causes can include thyroid conditions and iron deficiency.”

– British Association of Dermatologists, Telogen effluvium

So two things come first. Ferritin, the protein that holds iron in reserve, which is why it shows how much iron you have banked. And thyroid function, usually TSH with Free T4. Vitamin D and B12 are the common additions when the shedding has run for months.

Note what the BAD does not say. It does not call bloods the diagnosis. The diagnosis comes from your scalp and your history, and the blood test is there to rule other causes in or out. If your shedding started after a stressful stretch, our energy and fatigue hub covers the markers that move with it.

3. Ferritin: the most overlooked hair loss marker

Ferritin is your body's iron storage protein. Your GP will flag it only if it drops below 15 μg/L (the diagnostic threshold for iron deficiency anaemia), but hair follicles start struggling at much higher levels. The number can also read higher than the range without meaning too much iron, because ferritin climbs with inflammation. Hair fall and feeling itchy sit in the same NHS list of less common iron symptoms.

The 70 μg/L figure comes from a 2002 review in Clinical and Experimental Dermatology, which recommended that level for women with increased hair shedding while saying plainly that the right threshold “is yet to be definitively established.” It is nearly five times the NHS's lower limit, so a result called normal can still sit well under it. Ferritin is also the steadier of the iron markers, since serum iron dips during a period while stores barely move.

Iron is also an acute-phase reactant, meaning ferritin can rise temporarily during infection or inflammation, masking a true deficiency. Testing ferritin alongside CRP gives a clearer picture. The same handful of deficiencies that thin hair tend to show in your skin first; our skin health blood test guide covers that side of the picture. If you have reached for a DHT blocker instead, our guide to whether saw palmetto lowers testosterone sets out what the trials actually found.

Age changes the odds here more than the range does. UK labs publish ferritin by sex rather than by age, and for women the figure that shifts is the menopause, not a birthday.

4. Thyroid function: TSH, Free T4, Free T3

The thyroid gland regulates metabolism in every cell, including hair follicle cells. Both hypothyroidism (underactive) and hyperthyroidism (overactive) cause hair loss. Thyroid disease is one of the most common treatable causes in the UK, affecting roughly 1 in 20 people according to the NHS.

The hallmark sign is diffuse thinning across the entire scalp, often accompanied by thinning of the outer third of the eyebrows. Hair becomes dry, brittle, and slow to grow. In hypothyroidism, the hair follicle cycle slows dramatically. More follicles enter the resting phase, and fewer new hairs replace those that shed.

Most GPs test only TSH. That catches overt thyroid disease. But it misses subclinical cases where TSH is technically “in range” (say 3.5–4.0 mIU/L) but Free T4 and Free T3 are at the bottom of their ranges. Hair loss can start well before a formal diagnosis is made.

Testing TSH, Free T4, and Free T3 together gives a complete thyroid picture. If thyroid antibodies (TPO, TgAb) are also raised, it may indicate Hashimoto's thyroiditis. This is the most common cause of hypothyroidism in the UK, and it frequently presents with hair loss before other symptoms appear.

5. Testosterone, SHBG, and DHT-driven hair loss

Androgenetic alopecia is the most common type of hair loss in both men and women. It is driven by dihydrotestosterone (DHT), a potent metabolite of testosterone. DHT binds to receptors on genetically susceptible hair follicles, causing them to miniaturise over time until they stop producing visible hair.

In men, the pattern is classic: receding temples and crown thinning. In women, it presents as diffuse thinning at the parting line. The NICE Clinical Knowledge Summary notes that androgenetic alopecia affects roughly 50% of men over 50 and up to 40% of women by menopause.

The key blood markers are total testosterone, sex hormone-binding globulin (SHBG), and the free androgen index (FAI). Low SHBG means more free testosterone is available for conversion to DHT, even if total testosterone is “normal.”

In women, elevated DHEA-S alongside low SHBG may point toward polycystic ovary syndrome (PCOS) , one of the most common causes of female hair loss and a condition frequently diagnosed through blood tests rather than imaging.

6. Vitamin D and the hair follicle cycle

Vitamin D receptors are present on hair follicle keratinocytes, and vitamin D plays a direct role in the anagen (growth) phase of the hair cycle. Low vitamin D is associated with telogen effluvium and alopecia areata. Multiple systematic reviews confirm this link, including a 2019 meta-analysis in the Dermatology and Therapy journal.

The UK is one of the worst countries in Europe for vitamin D deficiency. Public Health England estimates that 1 in 5 adults has a serum level below 25 nmol/L. A far larger proportion sits between 25–50 nmol/L. That range is technically “sufficient” by NHS standards, but it sits well below the 75–125 nmol/L range associated with good general health outcomes.

If you're losing hair in the UK, especially between October and April when UVB exposure is virtually zero, vitamin D should be one of the first markers you check.

7. Zinc, biotin, and B12

Zinc is essential for hair follicle protein synthesis and cell division. A study in the Annals of Dermatology found significantly lower serum zinc in patients with all types of hair loss compared to healthy controls. Zinc deficiency is common in vegetarians, vegans, and people with gut disorders that impair absorption.

Biotin (vitamin B7) is aggressively marketed for hair growth, but true biotin deficiency is rare in people with normal diets. The evidence for biotin supplementation in non-deficient individuals is weak. However, biotin supplements interfere with many blood test assays. A May 2023 safety letter agreed with the MHRA warns that thyroid results may be falsely increased or falsely decreased, which can lead to misdiagnosis. Stop biotin supplements at least 48 hours before any blood test. Our guide to biotin, hair and thyroid tests covers the evidence and the washout in full.

Vitamin B12 deficiency impairs red blood cell production, reducing oxygen delivery to hair follicles. It's especially common in vegans, older adults, and those on long-term proton pump inhibitors. A B12 level below 300 pmol/L may contribute to hair thinning, even though the NHS lower limit is 148 pmol/L.

8. Cortisol: when stress causes shedding

Telogen effluvium is sudden, diffuse hair shedding 2–4 months after a stressor. It is one of the most common reasons people seek help for hair loss. The trigger can be physical (surgery, illness, crash dieting) or psychological (bereavement, job loss, prolonged work stress).

A 2021 study published in Nature demonstrated for the first time that corticosterone (the mouse equivalent of cortisol) directly inhibits hair follicle stem cell activation, keeping follicles locked in the resting phase. The research showed that removing the stress hormone source caused hair to regrow. That is biological proof of what many people already suspected.

Blood cortisol has limitations (it fluctuates throughout the day), but a morning cortisol test can flag overt adrenal dysfunction. If your cortisol is high alongside hair loss, it suggests stress as a contributing or primary factor.

9. Full blood count and anaemia screening

A full blood count (FBC) checks haemoglobin, red cell count, MCV (mean cell volume), and other markers that reveal anaemia, a direct cause of reduced oxygen delivery to hair follicles.

Iron deficiency anaemia is the most common type in women of reproductive age, affecting roughly 1 in 4 women in the UK according to NHS data. But anaemia can also be driven by B12 deficiency (macrocytic anaemia) or chronic disease, which is why an FBC alone is not enough. You need ferritin, B12, and folate alongside it to understand the cause. Our guide to normal folate levels covers the last of those, including the band where a result is neither clearly low nor clearly fine.

“Less common symptoms of iron deficiency anaemia … include … hair loss – you notice more hair coming out when brushing or washing it.”

– NHS, “Iron deficiency anaemia” (2026)

Low MCV with low ferritin points to iron deficiency. High MCV with low B12 or folate suggests megaloblastic anaemia. Normal MCV with low ferritin is the sneaky one. Your haemoglobin may still be “fine,” but your iron stores are depleted and your hair is paying the price.

10. NHS ranges vs optimal ranges for hair health

This is where the gap between “clinically normal” and “optimal for hair growth” is widest:

You can sit comfortably inside every NHS range and still have ferritin at 22, vitamin D at 30, and TSH at 3.8. Many dermatologists would flag that combination as a probable contributor to hair loss. This is why testing against optimal ranges matters, not just diagnostic cutoffs.

11. Who should get a hair loss blood test?

Consider a blood test if you're experiencing any of the following:

• Noticeable increase in hair shedding lasting more than 6 weeks
• Visible thinning at the parting, temples, or crown
• Hair loss alongside fatigue, weight changes, or mood shifts (suggesting thyroid or iron issues)
• Post-partum shedding that hasn't resolved after 6 months
• Hair loss following a period of significant stress, illness, or crash dieting
• Family history of pattern baldness combined with early signs of thinning
• Vegetarian, vegan, or restrictive diet (higher risk of iron, B12, and zinc depletion)

The NICE guidelines for hair loss recommend a full blood count, ferritin, thyroid function, and (in women) androgens as initial investigations. Most of these are available through your GP , though getting all of them in a single appointment can require persistence.

12. GP blood test vs Helvy: what you actually get

13. What to do with your results

Hair loss treatment depends entirely on the cause your blood test reveals. Here are the most common findings and their evidence-based responses:

• Low ferritin (<70 μg/L): Iron supplementation (ferrous fumarate or bisglycinate for better absorption), typically 3–6 months to rebuild stores. Retest at 3 months. The NICE guideline on blood transfusion (NG24) covers oral iron dosing for deficiency.
• Underactive thyroid (TSH >4.2 or subclinical 2.5–4.2 with symptoms): See your GP for further investigation. Levothyroxine is the standard treatment for confirmed hypothyroidism. Hair typically improves 6–12 months after thyroid levels normalise.
• Low vitamin D (<75 nmol/L): Supplement with D3 (cholecalciferol). The NHS recommends 400 IU/day for maintenance, but correction doses of 2,000–4,000 IU/day are common in clinical practice for deficiency. Retest at 3 months.
• Elevated androgens / low SHBG: Discuss anti-androgen treatment with your GP or dermatologist. In men, finasteride or minoxidil may be appropriate. In women, spironolactone or combined oral contraceptives may help. Blood monitoring is recommended.
• Low B12 or folate: B12 supplementation (sublingual methylcobalamin or intramuscular injections for severe deficiency). Folate via diet or folic acid supplement. Both are straightforward to correct.
• Stress-related (elevated cortisol, normal everything else): The hair will typically regrow on its own once the stressor resolves. This can take 6–12 months. Addressing sleep, exercise, and stress management accelerates recovery.

14. Frequently asked questions