Hair loss: which tests reveal the real cause

In shortFor hair loss, test: ferritin — hidden iron deficiency, the most common reversible cause in women; TSH — both hypo- and hyperthyroidism increase shedding; vitamin D — its deficiency is linked to diffuse hair loss. Additionally: a complete blood count, zinc and B12 as ordered, and in women with signs of hormonal imbalance — testosterone and prolactin. Tests first, shampoos second.

Why hair suffers first

The hair follicle needs resources, but it stands last in the queue for them: when iron, protein, or vitamins run short, the body supplies heart and brain first and switches hair to economy mode. Two to three months after the resource crash, shedding begins.

That delay is the key to diagnosis: recall what happened 2–3 months ago — illness, a diet, stress, childbirth. And take the tests: unlike memories, they show deficiencies that persist to this day.

Ferritin: the main test for hair loss

Hidden iron deficiency is cause number one of diffuse shedding in women, and hemoglobin is no help here: it falls last, when stores have long been empty. So the first test is ferritin — hair specialists aim for levels well above the bottom of the reference range.

If ferritin is low, the doctor prescribes iron for months — the hair cycle is slow, and patience is part of the treatment. A complete blood count is added to see the full red-cell picture.

Thyroid and vitamin D

The thyroid sets the renewal speed of all tissues, including follicles: both a shortage and an excess of its hormones increase shedding. TSH is a mandatory line with hair loss; if it deviates, the doctor adds free T4 and TPO antibodies.

Vitamin D takes part in the follicle cycle, and its deficiency is statistically linked to diffuse hair loss. Given that deficiency is found in most people in northern latitudes, a 25(OH)D test with hair loss is almost always justified.

Hormones — by indication

If a woman's shedding follows a male pattern — receding temples and a widening part — and comes with acne, facial hair, and a broken cycle, the doctor orders testosterone and prolactin: that is the picture of possible hyperandrogenism, and it is treated differently from deficiencies.

Not everyone needs a hormone panel: without symptoms of imbalance, random numbers only confuse. The right order is ferritin, TSH, vitamin D, a blood count — and only then, with grounds, hormones.

The minimum test set for hair loss

Ferritin — priority one, especially for women
TSH — the thyroid increases shedding in both directions
Vitamin D (25(OH)D) — deficiency is linked to diffuse loss
Complete blood count — anemia and inflammation
Testosterone and prolactin — only with signs of hormonal imbalance

Markers covered in this article

Ferritin Iron (serum)TSH (thyrotropin)Vitamin D Prolactin Testosterone Vitamin B12 Hemoglobin

Several markers on your report?

See how MedProtect explains results in the app: the whole report, a check of the recognized values, and a clear breakdown.

Get your results explained See an example

Frequently asked questions

How many hairs a day is normal?

A landmark is up to 100 hairs a day, more on washing days. If hair stays in clumps on the pillow, in the shower drain, and in tufts on the brush — that is already a reason for tests, not counting.

Do anti-hair-loss shampoos and ampoules help?

With iron deficiency or hypothyroidism — no: the problem is inside, not on the scalp. Cosmetics can improve the look of remaining hair, but only correcting the found deficiency or illness stops the cause.

When should I expect results from treatment?

The hair cycle is slow: shedding stops first after 1–2 months, then new undercoat becomes visible after another 2–3 months. Judging earlier is like checking sprouts a day after sowing.

Sources

Ferritin Blood Test: MedlinePlus Medical Test — MedlinePlus, National Library of Medicine. Accessed: August 29, 2026.
Ferritin blood test: MedlinePlus Medical Encyclopedia — MedlinePlus, National Library of Medicine. Accessed: August 29, 2026.
Iron Tests: MedlinePlus Medical Test — MedlinePlus, National Library of Medicine. Accessed: August 29, 2026.
Serum iron test: MedlinePlus Medical Encyclopedia — MedlinePlus, National Library of Medicine. Accessed: August 29, 2026.