Hair Loss Blood Test UK: 8 Markers to Check

Hair loss affects approximately 8 million women and 6.5 million men in the UK. While genetics plays a role, a significant proportion of hair loss has an underlying medical cause that a simple blood test can identify. Iron deficiency, thyroid dysfunction, hormonal imbalances, and vitamin deficiencies are all common treatable triggers — and they all show up in bloodwork.

The problem is that most people never get the right tests. A GP might check your thyroid and full blood count but overlook ferritin, zinc, or vitamin D — three markers with strong links to hair shedding. This guide covers the eight blood markers that dermatologists and trichologists recommend for investigating hair loss, what each one tells you, and which patterns they help diagnose.

The 8 Blood Markers for Hair Loss

These are the markers most commonly requested by dermatologists and trichologists in the UK when investigating hair shedding or thinning.

Let’s look at each marker in detail.

1. Ferritin — Iron Stores

Ferritin measures your body’s iron reserves and is the single most important blood marker for hair loss in women. Hair follicles are among the fastest-dividing cells in the body and are highly sensitive to drops in iron availability.

The NHS considers ferritin “normal” from around 15 µg/L upwards. However, trichology research shows that hair regrowth is optimised when ferritin reaches at least 70 µg/L. A study in the European Journal of Dermatology found antiandrogen treatments for female pattern hair loss were significantly more effective when ferritin was above 40 µg/L, while other research puts the optimal threshold at 70 µg/L.

This gap between “normal” and “optimal” is why many women are told their blood tests are fine when their hair is actively falling out. Heavy periods, vegetarian or vegan diets, pregnancy, and endurance exercise are common reasons for low ferritin.

2. TSH + Free T4 — Thyroid Function

Both hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid) disrupt the hair growth cycle and cause diffuse thinning across the scalp. TSH is the standard screening test — a level above 4.0 mIU/L suggests hypothyroidism, while a very low TSH may indicate hyperthyroidism.

However, TSH alone is not sufficient. You also need Free T4 and ideally Free T3 for a complete picture. Adding TPO antibodies can identify Hashimoto’s thyroiditis — the most common cause of hypothyroidism in the UK and a frequent driver of hair loss in women over 40.

The good news: thyroid-related hair loss is typically reversible once hormone levels are normalised. See our full thyroid blood test guide for more detail.

3. Vitamin D

Vitamin D plays a critical role in immune regulation and the hair follicle growth cycle. A 2024 systematic review in Frontiers in Nutrition found that 51.9% of alopecia areata patients and 53.5% of telogen effluvium patients were vitamin D deficient. The odds of deficiency were 2.84 times higher in alopecia areata patients compared to healthy controls.

Vitamin D receptors are expressed in hair follicle keratinocytes and are involved in the anagen (growth) phase of the hair cycle. Deficiency can trigger follicles to prematurely enter the resting phase, leading to increased shedding. Given that the UK’s latitude limits natural vitamin D synthesis from October to March — and Public Health England estimates 1 in 5 adults has low levels — this is an essential marker to check.

4. Vitamin B12

Vitamin B12 is essential for red blood cell production and oxygen delivery to tissues. Hair follicles depend on a steady oxygen supply — when B12 is low, red blood cell production falters and follicles may not receive adequate oxygen.

Some studies have found that up to 60% of chronic telogen effluvium patients had B12 deficiency compared to 26% of controls. While B12 deficiency alone may not be the primary driver, it is often found alongside other deficiencies (iron, vitamin D, folate) and should be checked as part of a comprehensive panel. Vegans, vegetarians, people over 50, and those taking proton pump inhibitors are at highest risk.

5. Zinc

Zinc is critical for the synthesis of keratin — the structural protein that makes up 95% of your hair shaft. A study in Healthcare found significantly lower serum zinc levels in hair loss patients (mean 84.33 µg/dL) compared to controls (97.94 µg/dL), and oral zinc supplementation has been shown to help resolve telogen effluvium in patients with confirmed deficiency.

Zinc deficiency is more common than many people realise in the UK, particularly among vegetarians, people with inflammatory bowel disease, and those on restrictive diets.

6. Testosterone + DHT — Androgens

DHT (dihydrotestosterone) is the primary hormonal driver of androgenetic alopecia. The enzyme 5-alpha reductase converts testosterone into DHT, which binds to androgen receptors in genetically susceptible follicles and causes them to miniaturise — producing progressively finer, shorter hairs until the follicle stops producing visible hair.

Overall testosterone levels do not necessarily predict hair loss. Follicle sensitivity to DHT, determined by genetic variations in androgen receptors, explains why two people with identical testosterone levels can experience very different hair loss patterns. Testing both testosterone and DHT, alongside SHBG (below), gives a more complete picture than any single marker.

7. SHBG — Sex Hormone-Binding Globulin

SHBG is a liver protein that binds testosterone and controls how much circulates in its free, active form. Low SHBG means more free testosterone available for conversion to DHT, accelerating androgenetic alopecia.

Research in the Journal of Clinical Endocrinology & Metabolism confirms that female pattern hair loss severity is negatively correlated with SHBG levels — the lower the SHBG, the worse the hair loss. Low SHBG is also a hallmark of PCOS, which is why hair thinning is one of the most distressing symptoms for women with this condition. SHBG is frequently overlooked in standard panels, yet it is essential for interpreting testosterone results.

8. CRP — C-Reactive Protein

CRP is a marker of systemic inflammation. Elevated CRP has been found in patients with alopecia areata (an autoimmune condition causing patchy hair loss) and scarring alopecia (where inflammation permanently destroys follicles). Research confirms CRP levels are significantly raised in alopecia areata patients relative to healthy controls.

If your hair loss is patchy, sudden, or accompanied by scalp tenderness or redness, CRP testing can help determine whether inflammation is driving the problem.

Types of Hair Loss and Which Markers Matter

Knowing which type of hair loss you are dealing with helps prioritise which markers to check first.

Many people experience more than one type simultaneously — for example, low ferritin plus undiagnosed PCOS could cause both telogen effluvium and androgenetic alopecia at once. This is why a comprehensive panel gives a clearer picture than testing one or two markers in isolation.

Women’s Hair Loss: Often Underdiagnosed

Hair loss in women is far more common than most people think — androgenetic alopecia alone affects approximately 40% of women by age 50 — yet it is frequently dismissed or underinvestigated.

The Ferritin Trap

Women of reproductive age lose iron through menstruation every month, and many have ferritin levels between 15 and 40 µg/L. GPs report this as “normal” because it sits above the laboratory reference range minimum — but hair follicles need ferritin above 70 µg/L to function optimally. Millions of women in the UK are told their iron is fine when it is actively contributing to their hair loss. If your ferritin is below 70, discuss targeted iron supplementation with your doctor.

The PCOS Connection

PCOS affects an estimated 1 in 10 women in the UK and is a major driver of female hair loss. Women with PCOS tend to have higher testosterone, elevated 5-alpha reductase activity, and lower SHBG levels — creating a hormonal environment that accelerates follicle miniaturisation. If you are experiencing thinning alongside irregular periods, acne, or weight gain, a blood panel including testosterone, SHBG, and DHT can help confirm or rule out a PCOS contribution.

The Menopause Link

As oestrogen levels decline during perimenopause and menopause, the relative influence of androgens increases — often leading to hair loss similar to androgenetic alopecia. Thyroid dysfunction also becomes more prevalent after 45. A comprehensive blood test covering thyroid, sex hormones, and nutrient levels is particularly valuable for women in their 40s and 50s. For more, read our menopause blood test guide.

Men’s Hair Loss: Beyond Genetics

Male pattern baldness affects around 66% of men by age 35 and 85% by age 50. It is driven primarily by genetic sensitivity to DHT — but assuming all male hair loss is “just genetics” can mean missing treatable factors.

DHT and Testosterone

In androgenetic alopecia, it is not the total amount of testosterone or DHT that matters most, but how sensitive your follicles are to DHT — determined by genetics. Testing DHT and testosterone is still useful, particularly when hair loss is rapid, diffuse, or accompanied by other symptoms.

Do Not Overlook Thyroid, Iron, and Zinc

Thyroid dysfunction, iron deficiency, and zinc deficiency can all cause or accelerate hair loss in men. If you are experiencing diffuse thinning rather than the typical receding pattern, check TSH, ferritin, and zinc in addition to androgen markers — especially if you are on a plant-based diet, train intensively, or are experiencing fatigue.

When to Get Tested

It is normal to lose 50–100 hairs per day. Consider a hair loss blood test if you notice any of the following:

• Increased shedding: Significantly more hair on your pillow, in the shower, or on your brush. Telogen effluvium can cause loss of up to 300 hairs per day.
• Visible thinning: A widening part, reduced ponytail thickness, or scalp showing through hair.
• Receding hairline or crown thinning: Classic androgenetic alopecia pattern.
• Patchy bald spots: Smooth, round patches that may indicate alopecia areata.
• Sudden onset after illness or stress: Hair loss 2–3 months after a major event often points to telogen effluvium.
• Hair loss with other symptoms: Fatigue, weight changes, irregular periods, or brittle nails suggest a systemic cause.

The sooner you test, the sooner you can identify a treatable cause. Many forms of hair loss are reversible when the underlying issue is corrected — but the longer follicles are deprived, the harder recovery becomes.

If you want a solid starting point that covers thyroid, iron, and key vitamins without the full hormonal panel, the Core Health 45 is a good alternative — though for hair loss specifically, the broader coverage of the Peak Insights 70 is recommended.

Frequently Asked Questions

What blood tests should I ask my GP for if I’m losing hair?

Ask for ferritin, TSH, Free T4, vitamin D, B12, zinc, and a full blood count as a minimum. If hormonal involvement is suspected, add testosterone, SHBG, and DHT. Many GP panels only include TSH and FBC, missing the most common nutritional causes.

Can a blood test diagnose the cause of hair loss?

Blood tests can identify treatable causes such as iron deficiency, thyroid dysfunction, and hormonal imbalances. Some hair loss (particularly androgenetic alopecia) is primarily genetic and may show normal results. Blood tests are most useful for ruling out or confirming metabolic and nutritional triggers.

What ferritin level is needed for healthy hair?

The NHS “normal” range starts at around 15 µg/L, but trichology research suggests ferritin should be above 70 µg/L for optimal hair growth. If yours is below 70, it may be contributing to shedding even if your GP says it is normal.

Can thyroid problems cause hair loss?

Yes. Both hypothyroidism and hyperthyroidism cause diffuse thinning by pushing follicles into the resting phase. Hashimoto’s thyroiditis is particularly associated with hair loss in the UK. Thyroid-related hair loss usually reverses once levels are stabilised.

Is hair loss from vitamin D deficiency reversible?

In most cases, yes. A 2024 study found significant improvement in hair shedding after three months of oral vitamin D supplementation. In the UK, where sunlight is limited for six months of the year, ongoing supplementation may be necessary.

How does PCOS cause hair loss?

PCOS causes elevated testosterone, increased 5-alpha reductase activity, and lower SHBG — resulting in higher DHT levels that miniaturise follicles. Thinning typically appears at the crown and along the part line.

Can men’s hair loss be caused by something other than genetics?

Yes. Thyroid dysfunction, iron deficiency, zinc deficiency, and chronic stress can all cause or accelerate hair loss in men. If your pattern is diffuse rather than the typical temple-and-crown recession, a blood test is recommended.

How long after fixing a deficiency will hair grow back?

Most people notice reduced shedding within 2–3 months, with visible regrowth at 4–6 months. Full recovery can take 6–12 months. Telogen effluvium from a single correctable cause (such as low ferritin) typically recovers fastest.