A focused set of blood tests, including ferritin, thyroid function, and vitamin D, can uncover treatable contributors to shedding. They are useful, but they cannot diagnose every type of hair loss on their own.
Blood tests are most helpful for diffuse shedding (telogen effluvium) and unexplained hair loss, where a hidden, treatable cause may be at play. They are less central for clear-cut pattern hair loss, which is usually diagnosed by examination. The aim is to find correctable problems, not to test everything indiscriminately.
Tests commonly worth doing
- Ferritin and full blood count: screens for iron deficiency and anaemia, a recognised contributor to shedding, especially in women.
- TSH (with free T4 if indicated): checks thyroid function, since both under- and over-active thyroid can cause hair loss.
- 25-hydroxyvitamin D: low levels are linked with several hair-loss types, particularly if you have deficiency risk factors.
- Vitamin B12 and folate: reasonable if your diet is restricted or you have absorption problems.
- Zinc: worth checking when deficiency is plausible, such as gut conditions or restrictive diets.
In some situations a clinician may add hormone tests (for example in women with signs of excess androgens) or other markers based on your history. Routine broad panels in everyone are not recommended, because incidental abnormal results can lead to unnecessary worry and treatment.
What tests cannot do
Normal blood tests do not rule out hair loss, and abnormal results do not always explain it. Many people have pattern hair loss with entirely normal bloods. Tests are a tool to find treatable contributors, not a substitute for a proper clinical assessment of your scalp and pattern of loss.
Getting the most from your tests
Bring a clear history to your appointment, including diet changes, weight loss, illnesses, new medicines, pregnancy, and family history, as this guides which tests are truly useful. Ferritin can be raised by infection or inflammation, so results are best read alongside the full picture rather than in isolation. If a deficiency is found and corrected, re-testing after a few months confirms whether treatment is working before you commit long term. See a dermatologist if loss is patchy, rapid, painful, or scarring, or if shedding persists despite normal results, because some causes need scalp examination, dermoscopy, or occasionally a biopsy rather than blood work alone.
Try the free self-check →FAQ
What is the single most useful blood test for hair loss?
There is no single test, but ferritin and thyroid function (TSH) are among the most commonly useful, as iron deficiency and thyroid problems are both treatable contributors to shedding. Vitamin D is often added too. The right panel depends on your history, so it is best chosen with a clinician.
My blood tests were normal but I'm still losing hair. Why?
Normal results do not rule out hair loss. Many causes, including pattern hair loss and some stress-related shedding, do not show up on blood tests at all. Tests are designed to catch treatable contributors, so a normal result simply points your clinician toward a clinical assessment of your scalp and pattern of loss.
Explore more
⚠️ When to see a doctor — don’t self-treat
- Sudden patchy or circular bald spots
- Redness, scaling, pus, pain or itch (possible scarring alopecia — treat urgently)
- Broken hairs or rapid loss
- Loss with body-wide signs (weight loss, fatigue, cycle changes, acne, extra hair)
- Loss right after a new medication
- Any hair loss in a child