Blood Tests for Hair Loss: What Could Be Causing It?

Noticing more hair in the brush or the shower drain can be worrying, and it’s natural to wonder whether a blood test for hair loss could explain what’s going on. Some causes of hair thinning are indeed reflected in your blood; low iron, thyroid problems, and certain vitamin or hormone imbalances among them. Others, like genetic (pattern) hair loss, are not.

When might hair loss have a medical cause?

Everyone sheds hair daily, and some thinning with age is normal. It’s worth looking deeper when hair loss is sudden, unusually heavy, patchy, or comes alongside other symptoms such as fatigue, weight change, feeling cold, or changes to your periods; because these can point to an underlying, often treatable, cause. Patchy loss or loss with scalp changes should be seen by a GP or dermatologist rather than relying on a blood test alone.

Causes a blood test can help explore

Low iron (ferritin)

Low iron stores are one of the most common contributors to diffuse hair thinning, especially in women with heavy periods or on plant-based diets. Ferritin reflects your iron stores and can be low before you’re anaemic, so it’s a key marker to check alongside a full blood count.

Thyroid problems

Both an underactive and an overactive thyroid can cause hair to thin. TSH, with Free T4 and Free T3, helps assess whether your thyroid is contributing, particularly if hair loss comes with fatigue, weight change or temperature sensitivity.

Vitamin D and B12

Deficiencies in vitamin D and vitamin B12 are common and have been linked with hair health. They’re easily measured and usually straightforward to correct.

Hormones and androgens

In women, raised androgens, sometimes associated with PCOS: can contribute to thinning, especially with irregular periods or acne. Markers such as testosterone and SHBG, alongside other hormones, can help build the picture. Hair changes around perimenopause are also common as oestrogen shifts.

What a blood test won’t tell you

Many cases of hair loss aren’t caused by anything measurable in blood. The most common type, male- and female-pattern hair loss: is largely genetic and won’t show on a test. Telogen effluvium, a temporary shedding that follows a stressful event, illness, childbirth or crash dieting, also typically has normal bloods and usually recovers on its own. Tight hairstyles, harsh treatments and some medications can play a role too. If your bloods are normal, that’s useful information; it points towards these causes and away from a hidden deficiency.

Which blood test should I consider?

• To check nutrient and iron levels: a Vitamin & Mineral Deficiency Test.
• If you suspect your thyroid: a Thyroid Function Test.
• If hormones or PCOS may be involved: a Hormone Profile.
• For a broad overview: a General Health & Wellbeing Screen.

Not sure which is right for you? Use our free Test Finder for a personalised recommendation in under a minute; no GP referral needed, with results reviewed by a GMC-registered doctor.

Frequently asked questions

Which blood tests are most useful for hair loss?

Ferritin (iron stores), full blood count, thyroid function, vitamin D and B12 are the usual starting points, with hormones added if PCOS or an androgen cause is suspected.

Can low iron really cause hair loss?

Low iron stores are a recognised contributor to diffuse thinning, which is why ferritin is one of the first things worth checking, especially in women with heavy periods.

My bloods are normal, why am I still losing hair?

Often it’s pattern (genetic) hair loss or temporary shedding after stress or illness, neither of which shows on blood tests. A GP or dermatologist can advise on these.

Should I see a doctor as well?

Yes, if hair loss is sudden, patchy, or accompanied by scalp changes; these should be assessed in person.

How soon will I get my results?

Most results are available within 1–2 working days and are reviewed by a GMC-registered doctor before you receive them.

Important note

This article is for general education only and is not medical advice or a diagnosis. Sudden, patchy or severe hair loss should be assessed by your GP or a dermatologist. Trupoint Health blood tests are analysed by a UKAS-accredited laboratory and reviewed by a GMC-registered doctor.

Medically reviewed by: ____________ (GMC-registered), pending review.