Iron, thyroid, vitamin D: the three blood tests worth asking your GP for

26 August 2026  ·  6 min read  ·  Reviewed for accuracy September 2026

Before anything else — before a serum, before a supplement, before a fringe — two conditions need ruling out, because they cause hair loss on their own and no hair product will touch them. Both are cheap to test for. Both are common in mums.

Ferritin, not just iron

Pregnancy and breastfeeding draw down iron stores, and two pregnancies close together can leave them low for years. The follicle is one of the first tissues to notice. Ask specifically for ferritin — the stored iron — rather than a general iron level or haemoglobin, which can both be normal while ferritin is low.

The reference range for ferritin starts somewhere around 15 to 30 depending on the lab, which is why so many women are told they are “normal”. For hair, most trichologists want to see ferritin above 70. If yours is 22, you are inside the range and your follicles are still short of iron. Ask for the number, not the verdict.

Thyroid: TSH and, if you can get it, free T4

Thyroid dysfunction is more common in women after pregnancy and around perimenopause, and an underactive thyroid produces exactly the diffuse thinning and texture change that gets blamed on hormones or stress. A TSH is standard; ask for it to be included and ask what the number was. Borderline results are worth repeating in three months rather than filing.

Vitamin D

Most of the UK is low from October to April, and the follicle has vitamin D receptors that matter for the growth cycle. It will not be the whole answer for anyone, but it is easy to correct and a genuine deficiency makes everything else harder.

How to ask

• Bring a photo of the parting or the hairline from a year or two ago, and one from now. It is the single most persuasive thing you can put in front of a GP.
• Say the words “I’d like ferritin, TSH and vitamin D checked, and I’d like to know the actual numbers.”
• If the shedding started suddenly after an illness, an operation, or a new medication, say so — that is a different condition (telogen effluvium) and it usually resolves on its own once the trigger is gone.

And if the bloods really are fine?

Then you have ruled out the two things that had to be ruled out, and what is left is the hormonal, follicle-level thinning that the rest of this site is about. That is not bad news. It means the problem is at the follicle, it has a mechanism, and the mechanism can be addressed. Start with reading the pattern.