HAIR RESTORATION
Blood Tests for Hair Loss: When They Help
When blood tests are useful for hair loss, which markers may be relevant, and why context matters more than a panel.
Not every patient with hair loss needs blood tests. Male pattern hair loss, for example, is usually diagnosed clinically from the pattern, onset and family history alone. But blood tests can be very useful when the clinical picture suggests a correctable contributor — iron deficiency, thyroid dysfunction, hormonal change, nutritional deficit, or a systemic condition that is affecting the hair alongside other symptoms. The key is testing for a reason, not ordering a broad panel without clinical reasoning.
Blood tests are most useful when they are chosen to answer a specific clinical question and interpreted within the context of the patient’s history and hair loss pattern.
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Which blood tests are commonly relevant
Ferritin and iron studies: Iron deficiency is one of the most commonly identified correctable contributors to hair thinning and shedding. Ferritin — the body’s iron storage marker — can be low enough to affect hair even when haemoglobin (the standard anaemia marker) is within normal range. Many dermatologists consider a ferritin level below 40–70 µg/L as potentially contributing to hair loss, even though laboratory reference ranges may accept lower values as “normal.” This is a common source of missed diagnosis.
Thyroid function (TSH, free T4): Both hypothyroidism and hyperthyroidism can cause hair thinning, textural changes, and increased shedding. Thyroid-related hair loss is often diffuse and may be accompanied by fatigue, weight change, cold intolerance, or mood disturbance.
Vitamin D, vitamin B12 and folate: Deficiencies in these are common in the UK and have been associated with hair thinning in some patients. Supplementation when levels are low is straightforward and may contribute to improvement alongside other measures.
Hormone testing: Testosterone, DHEA-S, SHBG and other androgen markers may be relevant in women with hair thinning alongside acne, excess body hair, or irregular periods — suggesting an androgen-related cause. In men, testosterone and free testosterone may be checked when hair loss sits alongside low testosterone symptoms. Oestrogen and progesterone may be relevant during perimenopause.
Understanding results
When blood tests do not explain the hair loss
Normal blood results do not rule out all causes of hair loss. Male pattern hair loss and female pattern hair loss are diagnosed clinically and usually produce normal blood tests. Telogen effluvium triggered by stress or illness may also produce normal results once the acute trigger has passed.
In these cases, blood tests serve to exclude correctable contributors rather than provide the diagnosis itself — which is still clinically valuable.
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Next steps
When to arrange testing
Blood tests are most worthwhile when hair loss is diffuse rather than patterned, when shedding has been sudden or disproportionate, when there are accompanying symptoms such as fatigue, weight change, cycle disruption, or mood change, or when there is a history of dietary restriction.
Patients who are not yet sure what they need should start with the hair restoration consultation — blood tests can be arranged during the same appointment if indicated.
Frequently asked questions
What blood tests should I ask for if I’m losing hair?
The tests that matter depend on your clinical picture. Commonly relevant markers include ferritin (iron stores), thyroid function (TSH and free T4), vitamin D, vitamin B12, and folate. Hormone testing — testosterone, DHEA-S, SHBG — may be appropriate for women with signs of androgen excess or men with broader hormonal symptoms. A GP who understands the clinical context will select the right panel rather than running a generic set.
Can normal blood results rule out a cause of hair loss?
Normal results rule out specific correctable contributors — but they do not rule out all causes. Pattern hair loss (androgenetic alopecia) typically produces entirely normal blood work. Normal results are still clinically useful: they confirm that deficiency, thyroid dysfunction, or hormonal imbalance are unlikely to be driving the problem, which narrows the diagnosis.
How long after correcting a deficiency should I expect hair improvement?
Hair growth is slow. Once a deficiency such as low ferritin or vitamin D has been corrected, it typically takes 3–6 months before reduced shedding becomes noticeable, and 6–12 months before meaningful regrowth is apparent. Patience and follow-up testing to confirm levels have normalised are both important.
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