Blood Tests for Hair Loss: What to Ask Your Doctor For

Blood tests aren’t always necessary for hair loss, but when they are, they’re high-value. The classic case is diffuse shedding in a woman, where a few targeted blood tests can identify a treatable contributor (low iron, thyroid disease, vitamin D deficiency, PCOS) that, untreated, will keep the shedding going regardless of what topical or oral hair-loss treatment you try.

This guide covers the high-yield panel, what each test means, the cutoff values that matter for hair specifically (which are sometimes stricter than the general lab “normal” range), and how to ask your GP for the workup if they’re hesitant.

When blood tests matter (and when they don’t)

Most cases of obvious androgenetic alopecia in a man (gradual temple/crown recession, positive family history, no other symptoms) don’t need bloods. The diagnosis is clinical and the treatment doesn’t change based on a panel.

Bloods are high-yield in:

• Diffuse hair loss. Whole-scalp thinning, especially in women.
• Hair loss disproportionate to age and family history.
• Hair loss plus other systemic symptoms. Fatigue, weight changes, period changes, cold intolerance, skin/nail changes, mood changes.
• Restrictive eating patterns. Vegetarianism without B12 supplementation, veganism, eating disorders, post-bariatric surgery.
• Heavy menstrual bleeding. A common driver of low ferritin.
• Telogen effluvium that hasn’t resolved by 6 months.
• Suspected female pattern hair loss with androgen-excess symptoms.

If your hair loss looks like classic male pattern, no other symptoms, and you’re starting minoxidil or finasteride, bloods aren’t strictly necessary. Useful as a baseline before starting oral medication, but not needed to confirm the diagnosis.

The high-yield panel, test by test

Ferritin (iron stores)

The single most useful blood test for hair loss in most clinical contexts. Ferritin reflects iron stores: the iron banked in your body, distinct from the iron currently circulating in blood (which is what serum iron and haemoglobin measure).

• What “normal” labs say: usually ferritin above 15–30 ng/mL is “in range.”
• What hair specialists say: target above 50 ng/mL; many target above 70 for active hair loss. Below 30 is a red flag for hair shedding even with normal haemoglobin.
• Why this matters: low ferritin can prolong telogen effluvium and worsen FPHL, and the relationship operates in a range labs often consider “normal”² .
• Treatment: oral iron supplementation (ferrous sulfate, ferrous fumarate, or gentler forms like iron bisglycinate) at doses appropriate to the deficiency. Re-test ferritin in 3 months. Address the underlying cause if it’s heavy menstrual bleeding or absorption issues.

TSH (thyroid-stimulating hormone), with free T4 if abnormal

Both hyper- and hypothyroidism cause hair loss³ . TSH is the screening test; free T4 and sometimes free T3 are added if TSH is abnormal.

• What “normal” labs say: TSH 0.4–4.0 mIU/L is the typical reference range.
• What hair specialists say: same range usually applies; subclinical thyroid disease (TSH at the high end of normal with normal T4) is sometimes worth investigating for hair loss specifically.
• Why this matters: thyroid hair loss is treatable. Thyroid disease is also overrepresented in women with autoimmune conditions including alopecia areata.
• Treatment: levothyroxine for hypothyroidism, antithyroid medication for hyperthyroidism. Hair recovery follows thyroid normalisation, often with a delay of months.

If you’ve been told you have “subclinical hypothyroidism” and have hair loss, it’s worth a discussion about whether treatment is appropriate.

Complete blood count (CBC)

A general overview that picks up anaemia (low haemoglobin), abnormal white cell counts (which could suggest a chronic illness contributing to hair loss), and other systemic clues. Inexpensive, almost always done as part of any workup.

Vitamin D (25-hydroxyvitamin D)

Vitamin D plays a role in the hair follicle cycle. Low vitamin D is associated with several hair loss conditions, including AGA, telogen effluvium, and alopecia areata⁵ .

• What “normal” labs say: above 20 ng/mL is “sufficient” by some guidelines; above 30 ng/mL by others.
• What hair specialists say: target above 30 ng/mL, often 40–50.
• Why this matters: deficiency is common (especially in northern latitudes, in winter, or in people who avoid sun exposure), and supplementation is cheap and safe.
• Treatment: vitamin D3 supplementation, dosed to deficiency severity. 1,000–2,000 IU daily for mild deficiency; higher doses (often 50,000 IU weekly for 8–12 weeks) for severe deficiency, then maintenance.

Vitamin B12

Most relevant in vegetarians, vegans, people with absorption issues (post-gastric surgery, atrophic gastritis), older adults, and those on long-term proton pump inhibitors¹ .

• Cutoff: above 200 pg/mL is “normal” but values 200–400 may be functionally low; many labs and clinicians use 400 as a more useful threshold for hair and neurological function.
• Treatment: oral cyanocobalamin or methylcobalamin for typical deficiency; intramuscular B12 for absorption issues.

Zinc

Zinc deficiency can cause hair loss, but it’s less commonly the answer than iron, thyroid, or vitamin D. Most relevant in restrictive eaters or people with chronic GI disease.

• Cutoff: below 70 mcg/dL is generally low.
• Treatment: zinc supplementation, with attention to copper levels (long-term high-dose zinc depletes copper).

Add-on tests for women with androgen excess

If a woman has hair loss plus signs of androgen excess (acne, irregular periods, hirsutism such as excess facial or body hair, or central weight gain) additional hormonal tests are worth adding:

• Total testosterone. Elevated suggests an androgen source (most often PCOS).
• Free testosterone. Sometimes more useful than total in certain contexts.
• DHEAS. Adrenal androgen marker.
• Prolactin. High prolactin can drive hair loss and irregular periods through several mechanisms.
• 17-hydroxyprogesterone, if non-classical congenital adrenal hyperplasia is suspected.
• Sex hormone-binding globulin (SHBG). Affects how much testosterone is bioavailable.

Bloods alone don’t diagnose PCOS (the full workup includes ovarian imaging and a clinical picture), but the hormonal panel often points toward whether further investigation is warranted. Covered in our female pattern hair loss guide.

Tests that often appear but matter less

A few tests commonly show up on “hair loss panels” sold by online clinics that have less evidence behind them:

• Heavy metals (mercury, lead, arsenic). Relevant only with specific exposure histories, not routine.
• Cortisol. Rarely the answer. Cushing’s syndrome can cause hair loss, but usually with other obvious clinical features (central weight gain, easy bruising, etc.).
• Comprehensive food sensitivity panels. Not useful for hair loss in the absence of clear clinical food reactions.
• Comprehensive amino acid panels. Same.
• Saliva hormone testing. Low evidence base; hormones for hair loss workup should be measured in blood.

If a clinic is offering you a 30-test “advanced hair loss panel” for several hundred dollars, ask whether each test changes the management plan. The high-yield panel is short, cheap, and most of what matters.

Cutoff values, side by side

How to ask your GP for the panel

Some GPs are generous with hair-loss workups. Some aren’t, particularly if hair loss is the only symptom. A few practical points:

• Frame it as a screen for treatable causes. “I’m experiencing diffuse hair shedding and want to rule out treatable contributors: iron deficiency, thyroid dysfunction, vitamin D deficiency.”
• Mention duration. Shedding for 3+ months is a reasonable threshold for workup.
• Mention any other symptoms. Fatigue, period changes, weight changes, cold intolerance, or mood changes all strengthen the case for a broader panel.
• Ask for ferritin specifically. GPs sometimes order serum iron or haemoglobin instead. Ferritin is the relevant test for hair loss.
• If declined, explain you’re willing to pay for private testing if NHS/insurance won’t cover it. Many people end up doing this; private hair-focused panels are widely available, though shop carefully (see “tests that matter less” above).

If your GP doesn’t take the request seriously and the loss is persistent, consider asking for a dermatology referral. A dermatologist will typically order the relevant panel as part of the workup.

When the bloods come back “normal”

Often they will. That’s a useful result. It rules out treatable contributors and shifts the focus to other causes (pattern hair loss, persistent telogen effluvium, alopecia areata, scarring alopecias).

If your bloods are clean and shedding continues, the next step is usually a dermatologist’s evaluation: trichoscopy (scalp magnification), pull test, sometimes a biopsy⁴ . The combination of clean bloods plus dermatology examination usually narrows the cause to something specific.

A common letdown: bloods are “normal” by lab standards but ferritin is 35 ng/mL or vitamin D is 25 ng/mL. By hair-specialist standards, both warrant treatment. It’s worth a conversation with the ordering doctor, or a dermatologist, about whether values are optimal or just within range.

When to see a doctor

• Persistent diffuse shedding for more than 3 months
• Hair loss plus any other symptoms (fatigue, weight changes, period changes, cold intolerance, skin/nail changes, mood changes)
• Hair loss in a woman with signs of androgen excess (acne, irregular periods, hirsutism)
• Restrictive eating, vegetarian/vegan without supplementation, or post-bariatric surgery
• Heavy menstrual bleeding that may be driving iron deficiency
• Bloods that come back showing values in the “normal but low” range, where it’s worth discussing whether to treat
• You’re starting prescription hair-loss treatment and want a baseline

What this article doesn’t cover

We’ve focused on the standard blood-test workup for non-emergent hair loss in adults. We haven’t covered the workup for paediatric hair loss, specific autoimmune disease panels (which are sometimes ordered when scarring alopecia is suspected), or the niche tests appropriate for unusual presentations. We also haven’t covered nutrition strategy in detail; that’s worth its own piece.

If hair loss is affecting your wellbeing, talk to a GP or dermatologist sooner rather than later. The right blood tests are part of a workup, not a substitute for one. Anything in this article is general education, not personal medical advice.