A blood test for hair loss is often one of the first steps a GP takes when investigating persistent or diffuse hair shedding. Hair loss — known medically as alopecia — can stem from a wide range of causes, including thyroid disorders, iron deficiency, hormonal imbalances, and nutritional deficiencies, many of which are identifiable through targeted blood tests. Understanding which tests are used, what the results mean, and what happens next can help you navigate your diagnosis with confidence. This guide covers the key investigations used in the UK, how results are interpreted, and the treatment pathways available on the NHS and privately.
Summary: A blood test for hair loss is a panel of investigations used to identify treatable systemic causes of hair shedding, such as thyroid disorders, iron deficiency, or hormonal imbalances.
- Common first-line tests include full blood count (FBC), serum ferritin, and thyroid function tests (TSH with reflex free T4), in line with NICE NG145.
- Low serum ferritin — indicating depleted iron stores — is one of the most frequently identified contributors to diffuse hair shedding, particularly in women of reproductive age.
- Both hypothyroidism and hyperthyroidism can cause diffuse hair thinning; treating a confirmed thyroid condition typically leads to gradual hair regrowth over six to twelve months.
- Normal blood test results do not exclude all causes of hair loss; scarring alopecia and androgenetic alopecia require clinical examination and may warrant dermatology referral.
- Private blood testing is available in the UK but should be conducted by CQC-regulated providers using UKAS-accredited laboratories, with results reviewed by a qualified clinician.
- Topical minoxidil is licensed over the counter in the UK for androgenetic alopecia in both men and women; finasteride is a prescription-only option licensed for male pattern hair loss in men.
Table of Contents
- Why a Blood Test May Be Recommended for Hair Loss
- Which Blood Tests Are Used to Investigate Hair Loss in the UK
- What Your Results Could Mean for Hair Loss Diagnosis
- Conditions Identified Through Blood Tests That Cause Hair Loss
- Getting a Hair Loss Blood Test on the NHS or Privately
- Next Steps After Your Blood Test Results
- Frequently Asked Questions
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Why a Blood Test May Be Recommended for Hair Loss
GPs recommend blood tests for hair loss to identify or rule out treatable systemic causes — such as thyroid disorders or iron deficiency — that may be contributing to diffuse or persistent shedding.
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Hair loss — medically referred to as alopecia — affects millions of people in the UK and can arise from a wide range of causes, including genetic factors, hormonal imbalances, nutritional deficiencies, and underlying medical conditions. When hair loss is diffuse (affecting the whole scalp rather than in patches), persistent, or accompanied by other symptoms such as fatigue, weight changes, or skin problems, a GP will often recommend a blood test as part of the initial investigation.
A blood test for hair loss is not a single, definitive test. Rather, it is a panel of investigations designed to identify or rule out systemic causes that may be contributing to excessive shedding or thinning. This is particularly important because many treatable conditions — such as thyroid disorders or iron deficiency — can cause significant hair loss that may be fully or partially reversible once the underlying cause is addressed.
It is worth noting that the most common form of hair loss in both men and women — androgenetic alopecia (pattern baldness) — is primarily genetic and hormonal in nature, and blood tests may return entirely normal results in these cases. However, a thorough blood workup helps ensure that no correctable medical cause is being overlooked before a diagnosis of pattern hair loss is confirmed.
A common and important cause of diffuse shedding is telogen effluvium — a temporary increase in hair loss that typically occurs two to three months after a significant trigger such as a serious illness, surgery, childbirth, rapid weight loss, or starting a new medicine. Your GP will consider your full clinical picture, including your medical history, diet, stress levels, and any medications you are taking, before deciding which tests are appropriate.
When to seek prompt assessment: If you notice a painful, inflamed, or rapidly scarring scalp, tufting of hairs, or significant redness and scaling — particularly in children, where tinea capitis (scalp ringworm) must be excluded — contact your GP promptly rather than waiting for routine blood results. These features may indicate a scarring alopecia or infection requiring urgent or expedited dermatology assessment, and blood tests alone are not sufficient to evaluate these conditions. Further information is available from the NHS hair loss page and NICE Clinical Knowledge Summaries (CKS) on alopecia.
| Blood Test | What It Measures | Relevance to Hair Loss | When Requested | Key Interpretation Notes |
|---|---|---|---|---|
| Full Blood Count (FBC) | Red/white blood cells, haemoglobin, platelets | Identifies anaemia or chronic illness contributing to diffuse shedding | First-line; most presentations of diffuse hair loss | Anaemia alone does not confirm cause; interpret alongside ferritin |
| Serum Ferritin | Iron stores in the body | Low ferritin is a frequent contributor to diffuse shedding, especially in women | First-line; routine in diffuse hair loss | Acute-phase reactant; may be falsely normal with inflammation — check CRP/ESR |
| Thyroid Function Tests (TFTs) | TSH with reflex free T4 | Both hypothyroidism and hyperthyroidism can cause diffuse hair thinning | First-line; in line with NICE NG145 | Subclinical thyroid disease requires clinical judgement; free T3 rarely needed |
| Vitamin D | 25-hydroxyvitamin D serum level | Deficiency associated with hair follicle cycling; common in UK population | When deficiency clinically suspected; per NICE CKS guidance | Direct causal link to hair loss not yet fully established in guidelines |
| Vitamin B12 & Folate | B12 and folate serum levels | Deficiencies can contribute to hair thinning, especially in plant-based diets | When dietary deficiency or malabsorption suspected | Particularly relevant in vegans, vegetarians, or those with GI conditions |
| Hormonal Profile (Testosterone, SHBG, FAI) | Total testosterone, sex hormone-binding globulin, free androgen index | Assesses androgen excess; relevant to PCOS-related female pattern hair loss | Women with acne, irregular periods, or signs of androgen excess | Interpret alongside clinical assessment; pelvic ultrasound may also be needed |
| Coeliac Serology (tTG IgA ± total IgA) | Tissue transglutaminase antibodies | Coeliac disease can cause malabsorption leading to iron deficiency and hair loss | Unexplained iron deficiency or GI symptoms; per NICE NG20 | Total IgA must be checked to exclude IgA deficiency causing false-negative result |
Which Blood Tests Are Used to Investigate Hair Loss in the UK
First-line investigations typically include full blood count, serum ferritin, and thyroid function tests; additional tests such as vitamin D, hormonal profile, or coeliac serology are ordered based on clinical presentation.
In the UK, GPs and dermatologists typically request a targeted panel of blood tests when investigating hair loss. The specific tests ordered will depend on your symptoms, medical history, and clinical examination. The following are the most commonly used investigations, grouped by how routinely they are requested:
First-line tests (commonly requested in most presentations of diffuse hair loss):
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Full blood count (FBC): Checks for anaemia and other blood cell abnormalities that may indicate nutritional deficiency or chronic illness.
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Serum ferritin: Measures iron stores in the body. Low ferritin is one of the most frequently identified contributors to diffuse hair shedding, particularly in women of reproductive age. Note that ferritin is an acute-phase reactant and may be falsely normal or elevated in the presence of inflammation; your GP may also check inflammatory markers (CRP or ESR) to help interpret the result.
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Thyroid function tests (TFTs): TSH (thyroid-stimulating hormone) with reflex free T4 is the standard primary care approach, in line with NICE NG145. Free T3 testing is rarely required at this stage. Both an underactive thyroid (hypothyroidism) and an overactive thyroid (hyperthyroidism) can cause hair loss.
Additional tests — requested when clinically indicated:
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Vitamin D: Deficiency is common in the UK population and has been associated with hair follicle cycling, though the direct causal link to hair loss remains an area of ongoing research. Testing is recommended where deficiency is clinically suspected, in line with NICE CKS guidance on vitamin D deficiency.
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Vitamin B12 and folate: Deficiencies in these nutrients can contribute to hair thinning and are particularly relevant in individuals following plant-based diets or those with malabsorption.
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Coeliac serology (tTG IgA ± total IgA): Should be considered where iron deficiency is unexplained or where gastrointestinal symptoms suggest coeliac disease, in line with NICE NG20.
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Hormonal profile: In women experiencing hair thinning with features suggestive of androgen excess (e.g., acne, irregular periods), tests may include total testosterone, sex hormone-binding globulin (SHBG), and free androgen index (FAI), alongside clinical assessment and pelvic ultrasound where appropriate, to assess for conditions such as polycystic ovary syndrome (PCOS). Prolactin may also be checked if clinically indicated. Routine measurement of LH and FSH is not recommended for PCOS diagnosis in primary care.
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Blood glucose and HbA1c: To screen for diabetes, which can affect hair growth, where clinically indicated.
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Inflammatory markers (ESR, CRP): May be requested if autoimmune or inflammatory conditions are suspected, or to contextualise ferritin results.
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Zinc levels: May be checked if dietary deficiency is suspected, though routine testing is not standard practice.
Your GP will tailor the panel to your individual presentation. The Primary Care Dermatology Society (PCDS) provides guidance on appropriate investigation of hair loss in primary care.
What Your Results Could Mean for Hair Loss Diagnosis
Results must be interpreted in clinical context; low ferritin, abnormal TSH, or vitamin D deficiency may explain hair loss, while normal results help narrow the diagnosis towards androgenetic alopecia or telogen effluvium.
Receiving your blood test results can feel overwhelming, particularly if values fall outside the standard reference range. It is important to understand that a result flagged as 'low' or 'high' does not automatically confirm a diagnosis — results must always be interpreted in the context of your symptoms and clinical history by a qualified healthcare professional.
Serum ferritin is a commonly discussed result in the context of hair loss. Some research suggests that hair shedding may occur even when ferritin levels are within the lower end of the normal laboratory range, though there is no universally agreed clinical threshold for hair loss specifically. Importantly, ferritin is an acute-phase reactant, meaning it can be falsely normal or elevated when inflammation is present. If your GP suspects this may be affecting interpretation, they may consider checking transferrin saturation or repeating the test once any acute illness has resolved, in line with BSG/BSH guidance on iron deficiency.
Vitamin D deficiency is widespread in the UK — particularly during autumn and winter — and while it has been associated with certain types of alopecia, the relationship is not yet fully established in clinical guidelines. The SACN report on vitamin D and NICE CKS guidance provide the current evidence base for testing and supplementation decisions.
Thyroid results require careful interpretation. A clearly elevated TSH indicating hypothyroidism, or a suppressed TSH indicating hyperthyroidism, provides a direct and actionable diagnosis, managed in line with NICE NG145. Subclinical thyroid disease (where TSH is mildly abnormal but free T4 remains normal) requires clinical judgement and may not always explain hair loss on its own. Treatment of a confirmed thyroid condition often leads to gradual improvement in hair loss over several months, though recovery is not always complete.
If all blood tests return within normal limits, this is clinically useful information. It helps to narrow the diagnosis towards androgenetic alopecia, telogen effluvium triggered by a past stressor, or a dermatological condition such as alopecia areata. However, it is important to note that normal blood tests do not exclude scarring alopecia. If clinical examination reveals features such as scalp inflammation, scarring, or follicular destruction, referral to a dermatologist remains appropriate regardless of blood test results. Normal results should not be dismissed as unhelpful; they guide the next steps in your care.
Conditions Identified Through Blood Tests That Cause Hair Loss
Blood tests can identify conditions including hypothyroidism, iron deficiency, PCOS, and autoimmune disorders such as coeliac disease or SLE, all of which can cause significant hair loss.
Several medically significant conditions that cause hair loss can be identified or supported through blood testing. Understanding these conditions can help patients engage more meaningfully with their diagnosis and treatment plan.
Hypothyroidism is one of the most common findings. The thyroid gland regulates metabolism, and when it is underactive, hair follicles may enter a prolonged resting phase, leading to diffuse thinning. Treatment with levothyroxine, guided by NICE NG145, typically leads to gradual hair regrowth over six to twelve months, though improvement is not guaranteed in all cases.
Iron deficiency — with or without frank anaemia — is particularly prevalent in women with heavy menstrual periods. A low serum ferritin strongly suggests depleted iron stores, though results should be interpreted alongside inflammatory markers (CRP/ESR), as ferritin can be falsely elevated in inflammatory states; transferrin saturation may be helpful where uncertainty remains, in line with BSG/BSH guidance. Supplementation under medical guidance can help restore hair density over time. Self-supplementing with high-dose iron without medical advice is not recommended, as excess iron carries its own health risks.
Polycystic ovary syndrome (PCOS) is a hormonal condition affecting approximately one in ten women in the UK. Diagnosis is based on the Rotterdam criteria, which require two of the following three features: irregular or absent ovulation, clinical or biochemical signs of androgen excess, and polycystic ovarian morphology on ultrasound. Blood tests measuring total testosterone, SHBG, and free androgen index (FAI) are used to assess biochemical hyperandrogenism, in line with NICE CKS guidance on PCOS. Elevated androgens can cause female pattern hair loss, as well as acne and irregular periods.
Autoimmune and other systemic conditions such as systemic lupus erythematosus (SLE) or coeliac disease may also present with hair loss. Targeted testing — such as ANA, anti-dsDNA antibodies, or coeliac serology (tTG IgA) — should be guided by clinical suspicion based on history and examination, rather than ordered routinely. Identifying these conditions is important not only for managing hair loss but for protecting overall long-term health. NICE NG20 provides guidance on the investigation of coeliac disease.
Getting a Hair Loss Blood Test on the NHS or Privately
NHS GPs can request hair loss blood tests free of charge; private testing is available through CQC-regulated providers, but results should always be reviewed by a qualified clinician.
In the UK, the first point of contact for investigating hair loss should be your NHS GP. If your hair loss is significant, progressive, or accompanied by other symptoms, your GP can request appropriate blood tests free of charge through the NHS. Waiting times for GP appointments and test results vary by region, but many practices make routine blood results available online through NHS-linked patient record services; availability depends on your GP practice and local system.
If your GP determines that your hair loss is likely androgenetic (pattern-related) and blood tests are normal, referral to a dermatologist on the NHS will depend on local commissioning arrangements and clinical need. Cosmetic hair loss may not meet the threshold for NHS dermatology referral in all areas. However, if an underlying medical condition is identified, or if alopecia areata or scarring alopecia is suspected, an NHS dermatology referral is likely to be appropriate.
For those who prefer faster access or more comprehensive testing, private blood testing is widely available in the UK through private GP clinics, private hospitals, and accredited laboratory services. It is important to choose a provider that is regulated by the Care Quality Commission (CQC) and uses laboratories accredited by the United Kingdom Accreditation Service (UKAS), which sets quality standards for medical testing. Ensure that any private results are reviewed by a qualified clinician rather than interpreted in isolation, as results without clinical context can lead to unnecessary anxiety or inappropriate self-treatment.
Be cautious of direct-to-consumer testing services that provide results without clinician review. If you are unsure whether a private provider meets appropriate quality standards, you can check the CQC register at cqc.org.uk.
Next Steps After Your Blood Test Results
If a deficiency or condition is found, treatment or specialist referral is initiated; if results are normal, management options include topical minoxidil, lifestyle advice, or dermatology referral if the diagnosis remains uncertain.
Once your blood test results are available, your GP will discuss the findings with you and recommend appropriate next steps. The pathway forward will depend largely on what — if anything — has been identified.
If a deficiency or medical condition is found, treatment will be initiated or a referral made to the relevant specialist. For example, thyroid conditions are managed by your GP or an endocrinologist in line with NICE NG145; PCOS may involve referral to a gynaecologist or endocrinologist; and autoimmune conditions may require rheumatology input. It is important to have realistic expectations — hair regrowth following treatment of an underlying cause is typically slow, often taking six months to a year before noticeable improvement occurs, and recovery may not always be complete.
If results are normal, your GP may diagnose telogen effluvium (a temporary, stress- or illness-related shedding that usually resolves without specific treatment) or androgenetic alopecia. In these cases, management options include:
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Topical minoxidil — licensed over the counter in the UK for both men and women as a treatment for androgenetic alopecia; it works by prolonging the hair growth phase. Follow the instructions on the product labelling carefully.
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Oral minoxidil — sometimes used for hair loss but is not licensed for this indication in the UK and would be prescribed off-label; this should only be considered under the supervision of a clinician with appropriate expertise.
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Finasteride — an oral prescription-only medicine licensed for male pattern hair loss in men. It should not be used by women of childbearing potential. Men considering finasteride should discuss the benefits and risks, including potential sexual side effects, with their prescriber. NICE CKS provides guidance on male pattern hair loss.
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Lifestyle advice — addressing nutritional gaps, stress management, and gentle hair care practices.
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Referral to a consultant dermatologist — if the diagnosis is uncertain, hair loss is rapidly progressive, or it is significantly affecting quality of life. If you choose to see a trichologist privately, be aware that trichology is not a statutorily regulated healthcare profession in the UK; where possible, seek assessment from an NHS GP or a GMC-registered dermatologist.
If you experience a suspected side effect from any medicine used to treat hair loss, you can report this to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk.
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When to seek prompt advice: Contact your GP promptly if you notice sudden or patchy hair loss, scalp inflammation, pain, or scarring, hair loss alongside significant systemic symptoms (such as unexplained weight loss, extreme fatigue, or joint pain), scaling or broken hairs in a child (which may suggest tinea capitis), or if hair loss is causing significant psychological distress. The British Association of Dermatologists (BAD) and Alopecia UK offer further patient information and support.
Frequently Asked Questions
Can a blood test tell me why my hair is falling out?
A blood test for hair loss can identify many common systemic causes, such as low iron stores, thyroid dysfunction, or hormonal imbalances, but it cannot diagnose every type of alopecia. Conditions like androgenetic alopecia and scarring alopecia require clinical examination and sometimes a scalp biopsy, so blood tests are one part of a broader assessment.
What ferritin level is considered too low for healthy hair?
There is no universally agreed ferritin threshold specifically for hair loss, but some research suggests shedding can occur even at the lower end of the normal laboratory range. Your GP will interpret your ferritin result alongside inflammatory markers such as CRP, as ferritin can be falsely normal or elevated when inflammation is present.
How long does it take for hair to grow back after treating the underlying cause?
Hair regrowth following treatment of an underlying cause — such as correcting a thyroid condition or iron deficiency — is typically slow, often taking six months to a year before noticeable improvement occurs. Recovery may not always be complete, so it is important to have realistic expectations and follow up with your GP or specialist.
Is there a difference between a blood test for hair loss in women compared to men?
The core first-line tests — full blood count, ferritin, and thyroid function — are used for both men and women, but women may also have hormonal tests such as testosterone, SHBG, and free androgen index if androgen excess or PCOS is suspected. Men are less commonly tested for hormonal causes unless there are specific clinical features suggesting an underlying endocrine condition.
Can I just buy a hair loss blood test online without seeing a GP?
Direct-to-consumer blood tests are available online in the UK, but results without clinician review can lead to unnecessary anxiety or inappropriate self-treatment. If you choose private testing, use a CQC-regulated provider with a UKAS-accredited laboratory and ensure a qualified clinician reviews and explains your results.
What is the difference between telogen effluvium and androgenetic alopecia?
Telogen effluvium is a temporary, diffuse shedding triggered by a stressor such as illness, surgery, or childbirth, and it usually resolves on its own within several months without specific treatment. Androgenetic alopecia — pattern baldness — is a genetic and hormonal condition causing progressive thinning that does not resolve spontaneously and may benefit from treatments such as topical minoxidil or, in men, finasteride.
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