Hair loss: which tests are worth doing?

Hair loss can be linked to nutritional deficiencies, hormonal disorders, thyroid disease, inflammation, medications, rapid weight loss, or a heavy strain on the body. Sometimes, however, its cause lies directly within the scalp and hair follicles.

That is why there is no single universal "hair loss test panel" that everyone should have done. The scope of diagnostics should be matched to the type of hair loss, how long the problem has lasted, accompanying symptoms, diet, chronic conditions, and medications being taken.

The best starting point is not ordering a dozen random tests, but a thorough history and an assessment of the scalp – ideally using trichoscopy.

First, determine the type of hair loss

A similar symptom can occur in several completely different problems.

Diffuse hair loss

Hair falls out across the whole surface of the head, often during washing, combing, or drying. This can correspond to telogen effluvium, which is sometimes linked to, among others:

• a recent infection or fever,
• surgery or another major strain on the body,
• childbirth,
• chronic stress,
• rapid weight loss,
• insufficient energy or protein intake,
• iron deficiency,
• thyroid dysfunction,
• starting or stopping certain medications.

Gradual thinning of the hair

A widening part, increasingly thin hair at the top of the head, and a gradual reduction in volume may point to androgenetic alopecia or female-pattern hair loss.

In this case, trichoscopy is very important. It allows assessment of, among others, differences in hair shaft diameter, the presence of miniaturized hairs, and the number of hairs growing from individual follicular units. In women, visual assessment alone may be insufficient.

Round or irregular patches without hair

Clearly defined, smooth areas without hair may suggest alopecia areata. In this case a broad laboratory panel is usually not necessary.

Current British Association of Dermatologists guidelines indicate that in most people with a typical picture of alopecia areata, routine blood tests are not needed. Tests are chosen individually, for example when the history or symptoms point to thyroid disease or another autoimmune condition.

Hair loss combined with skin inflammation

Pain, burning, intense itching, redness, scaling, pustules, scarring, or the disappearance of follicular openings require a dermatological consultation. They may indicate scarring alopecia or another scalp disease.

In this case, doing blood tests alone may delay the correct diagnosis. Sometimes a mycological examination, additional dermatological diagnostics, or a scalp biopsy is necessary.

Which tests are most often considered in diffuse hair loss?

1. Complete blood count

A complete blood count allows assessment of, among others, hemoglobin concentration, the number of red blood cells, and parameters such as MCV and MCH. It helps detect anemia, which can coexist with intense hair loss, weakness, exertional shortness of breath, impaired concentration, or chronic fatigue.

A normal complete blood count, however, does not rule out early iron deficiency. Iron stores can drop before full-blown anemia develops.

2. Ferritin and iron metabolism

Ferritin is one of the most commonly measured parameters in people with diffuse hair loss. It helps assess iron stores, but its result should be interpreted in a broader context.

Ferritin is also an acute-phase protein. It can be elevated during infection, chronic inflammation, in liver diseases, and in some metabolic disorders. In justified cases the doctor may therefore also order:

• iron,
• transferrin,
• total iron-binding capacity,
• transferrin saturation,

The latest meta-analysis from 2026 showed on average lower ferritin concentrations in people with telogen effluvium than in control groups. The authors, however, pointed out the substantial heterogeneity of the included studies. This means that a low ferritin level can be one of the important elements of diagnostics, but it will not be the main cause of the problem in everyone.

There is also no single scientifically confirmed "ideal ferritin level for hair". The values of 50, 70, or 100 ng/ml found online should not be treated as a universal treatment target. The result should be related to the whole clinical picture, the complete blood count, symptoms, the presence of inflammation, and the cause of any iron loss.

3. TSH, and fT4 if needed

Both hypothyroidism and hyperthyroidism can affect hair condition. Measuring TSH is worth considering especially when hair loss is accompanied by:

• chronic fatigue,
• drowsiness or agitation,
• intolerance of cold or heat,
• changes in body weight,
• heart rhythm disturbances,
• constipation or frequent bowel movements,
• dry skin,
• menstrual disturbances,
• thyroid disease in the personal or family history.

Not every TSH result in the upper part of the reference range is responsible for hair loss, however. In a 2026 study of people with various types of alopecia, no significant differences in TSH distribution were shown between patients with normal thyroid function. The result should therefore be interpreted together with symptoms and – if needed – with fT4 and further thyroid diagnostics.

Anti-TPO and anti-TG antibodies do not have to be measured automatically in everyone with hair loss. They are most useful when autoimmune thyroid disease is suspected.

4. Vitamin D – 25(OH)D

Observational studies often show lower vitamin D concentrations in people with some types of hair loss. In a meta-analysis published in 2026, lower 25(OH)D concentrations were also observed in people with telogen effluvium. The results of individual studies, however, were very heterogeneous.

Measuring 25(OH)D is worth considering primarily in the case of:

• limited sun exposure,
• not supplementing vitamin D,
• diseases causing malabsorption,
• osteopenia or osteoporosis,
• elimination diets,
• a previously confirmed deficiency.

A low vitamin D level may require correction, but it does not automatically mean it is the only cause of hair loss.

5. Vitamin B12 and folic acid

Measuring vitamin B12 and folic acid may be justified, among others, in people who:

• follow a vegan or very restrictive diet,
• have anemia or an abnormal MCV,
• have gastrointestinal diseases,
• have had bariatric surgery,
• take medications affecting vitamin B12 absorption,
• have neurological symptoms, weakness, or inflammation of the tongue.

There is, however, no strong basis for measuring these parameters routinely in everyone with hair loss.

6. Zinc

Zinc takes part in processes related to cell division and skin function, but its serum concentration is not an ideal indicator of the body's overall nutritional status.

A 2024 case-control study showed lower zinc concentrations in women with chronic telogen effluvium. At the same time, no differences were found between patients and the control group in hemoglobin, ferritin, vitamin B12, vitamin D, thyroid hormones, copper, or biotin. These results support individual rather than automatic ordering of broad micronutrient panels.

Measuring zinc can be considered with a restrictive diet, malnutrition, chronic diarrhea, malabsorption, wound healing, or other symptoms suggesting a deficiency.

When are hormonal tests worthwhile?

Sex hormone tests are not needed by every woman with hair thinning. A normal androgen concentration does not rule out female-pattern hair loss, and an abnormal laboratory result should be interpreted together with symptoms.

Diagnostics towards hyperandrogenism is worth considering especially when hair loss is accompanied by:

• irregular or disappearing periods,
• excessive facial or body hair,
• intense or suddenly appearing acne,
• difficulty conceiving,
• rapid progression of hair thinning,
• voice lowering or other signs of virilization.

According to the Society for Endocrinology guidelines from 2025, the scope of diagnostics may include, among others:

• total testosterone,
• SHBG and assessment of free testosterone,
• DHEA-S,
• androstenedione,
• 17-hydroxyprogesterone.

Androgen tests should be performed in the morning, ideally fasting and – if possible – in the early follicular phase of the cycle. The scope of tests and the way to prepare depend, however, on the clinical situation, the hormonal contraception used, and the aim of the diagnostics.

Rapidly increasing symptoms of hyperandrogenism or virilization require an urgent medical consultation, because they can rarely be linked to a more serious disease of the ovaries or adrenal glands.

Which tests are done only in specific situations?

Depending on symptoms, the doctor may also consider:

• celiac disease antibodies – with iron deficiency, chronic intestinal complaints, deficiencies, or weight loss;
• mycological examination – with skin scaling, broken hairs, itching, or suspicion of a fungal infection;
• tests for autoimmune diseases – only with characteristic symptoms;
• tests for syphilis – when the clinical picture or history justifies such a suspicion;
• scalp biopsy – with suspicion of scarring alopecia or when the diagnosis remains unclear.

Guidelines on alopecia areata emphasize that such tests should stem from a specific clinical suspicion, rather than being performed routinely "just in case".

What about biotin?

Biotin is often advertised as the basic supplement "for hair, skin, and nails". Its actual deficiency, however, is rare, and in a study of women with chronic telogen effluvium no lower biotin concentrations were found than in the control group.

Moreover, high doses of biotin can interfere with the results of some laboratory tests, including measurements of thyroid hormones, sex hormones, vitamin D, parathyroid hormone, and some cardiac markers. The effect depends on the dose, the time since taking the supplement, and the method used by the laboratory.

Before a blood draw, you should inform the doctor and the laboratory about taking biotin. You should not set the timing of stopping it on your own, because recommendations may differ depending on the dose and the type of test being performed.

A practical list of tests to start with

With diffuse, persistent hair loss, the doctor may first consider:

1. a complete blood count,
2. ferritin,
3. TSH, and fT4 if indicated,
4. CRP and a broader assessment of iron metabolism if the interpretation of ferritin is ambiguous.

Depending on diet, symptoms, and history, the scope can be extended to include:

• 25(OH)D,
• vitamin B12,
• folic acid,
• zinc,
• total protein and albumin,
• hormonal tests,
• tests for malabsorption or autoimmune diseases.

This does not mean that all of these parameters need to be done at once. A broad panel may generate random, borderline deviations that have nothing to do with hair condition.

Frequently asked questions

Is there a single ready-made test panel for hair loss?

No. The scope of tests should depend on the pattern of hair loss, the results of the scalp examination, accompanying symptoms, diet, medications, and health history. In androgenetic or scarring alopecia, a dermatological examination and trichoscopy may be more important than an extensive blood panel.

Does a normal complete blood count rule out iron deficiency?

No. Iron stores can be reduced before hemoglobin concentration drops. For this reason, ferritin is often measured as well in diffuse hair loss.

What ferritin level is best for hair?

No single, universal ferritin level guaranteeing normal hair growth has been established. The result should be interpreted together with the complete blood count, CRP, symptoms, periods, diet, and the other parameters of iron metabolism. Taking iron on your own solely to reach an online "target for hair" is not safe.

Do all hormones need to be tested in hair loss?

No. Androgen tests matter most when menstrual disturbances, hirsutism, intense acne, fertility problems, or rapid progression of symptoms are also present. In many women with female-pattern hair loss, hormone results remain normal.

Can a low vitamin D level cause hair loss?

Vitamin D deficiency can coexist with some types of hair loss, but it is not always their direct and only cause. Correcting a confirmed deficiency is important for general health, but it does not replace dermatological diagnostics.

Is it worth testing zinc, selenium, copper, and biotin straight away?

Not in everyone. These measurements are more justified with a restrictive diet, malnutrition, malabsorption, or other symptoms of deficiency. Current research does not confirm that all people with telogen effluvium have disturbed concentrations of these components.

Can you start supplementation before doing the tests?

It is better to first assess the diet and confirm actual indications. Iron, zinc, selenium, or vitamin A taken in excess can be harmful, and some supplements may paradoxically worsen hair loss. Biotin can additionally distort some laboratory results.

Do normal test results mean the problem is 'just from stress'?

No. Normal results do not rule out androgenetic alopecia, chronic telogen effluvium, alopecia areata, or scalp diseases. Stress can be one of the factors, but the diagnosis should stem from the history, the skin examination, and – if needed – trichoscopy.

Summary

Hair loss is a symptom, not a separate diagnosis. The most rational diagnostics start by determining the type of problem and assessing the scalp.

With diffuse hair loss, a complete blood count, ferritin, and an assessment of thyroid function are most often considered. Vitamin D, vitamin B12, folic acid, zinc, and hormones should be measured primarily when symptoms, diet, or health history argue for it.

The aim of the tests is not to find any result outside the range, but to determine whether there is a cause whose treatment can genuinely improve health and hair condition. It is worth remembering that persistent tiredness alongside hair loss can also stem from lifestyle factors rather than a clear diagnosis.

This material is educational in nature and does not replace an individual medical consultation or dermatological diagnostics.

References

1. Harries M.J. et al. British Association of Dermatologists living guideline for managing people with alopecia areata 2025. British Journal of Dermatology, 2025.
2. Elhassan Y.S. et al. Society for Endocrinology Clinical Practice Guideline for the Evaluation of Androgen Excess in Women. Clinical Endocrinology. 2025;103(4):540–566. doi: 10.1111/cen.15265.
3. Ahmed A. et al. Association between Serum Trace Elements and Telogen Effluvium: A Systematic Review and Meta-Analysis. Skin Appendage Disorders, 2026. doi: 10.1159/000550921.
4. Durusu Turkoglu I.N. et al. A comprehensive investigation of biochemical status in patients with telogen effluvium: Analysis of Hb, ferritin, vitamin B12, vitamin D, thyroid function tests, zinc, copper, biotin, and selenium levels. Journal of Cosmetic Dermatology, 2024. doi: 10.1111/jocd.16512.
5. Kuczara A. et al. Trichoscopy of Androgenetic Alopecia: A Systematic Review. Journal of Clinical Medicine. 2024;13(7):1962. doi: 10.3390/jcm13071962.
6. Zhang D., LaSenna C., Shields B.E. Serum Ferritin Levels: A Clinical Guide in Patients With Hair Loss. Cutis. 2023;112(2):62–67. doi: 10.12788/cutis.0837.
7. An Analysis of Thyrotropin Levels in Patients With Nonscarring Alopecia: A Single-Center Retrospective Comparative Study. Journal of Clinical and Aesthetic Dermatology. 2026;19(4):35–37.
8. Li D. et al. AACC Guidance Document on Biotin Interference in Laboratory Tests. Journal of Applied Laboratory Medicine. 2020;5(3):575–587. doi: 10.1093/jalm/jfz010.