The Blood Tests Your Hair Actually Needs (And Why Your GP Probably Didn't Run Them)

I can’t tell you how many clients have sat in my clinic and said, “But my doctor told me my bloods were fine.” They’re frustrated, they’re still shedding, and they don’t understand why nothing has changed. Nine times out of ten, the answer is the same: the right tests weren’t done.

That’s not a criticism of GPs — they’re working from a different checklist. But hair has its own set of nutritional demands, and a standard blood panel simply doesn’t cover them. If you want to understand what’s driving your shedding, you need to know what to ask for.

Why standard blood work misses what your hair needs

When your GP runs a routine blood test, they’re checking that your body is functioning safely. They’re looking for anaemia, infection, organ function, blood sugar — the essentials. And that’s exactly what they should be doing.

But here’s where hair gets overlooked: your body can be functioning well overall while your hair is quietly starving. That’s because hair is never a priority for your body. When nutrients are limited, they go to your heart, your brain, your immune system — the things that keep you alive. Hair gets what’s left over. Which means your levels can sit within the “normal” range on paper and still be far too low for your hair to grow properly.

This is the gap I see over and over again. Someone’s ferritin comes back at 25 and the GP says, “That’s normal.” And technically, for general health, it is. But for hair? It’s not even close.

The tests I recommend — and what each one tells us

These are the markers I check when a client comes to me with increased shedding. You can request most of these through your GP, or arrange them privately if you want a more focused panel.

Ferritin

This is my number one. Ferritin measures your stored iron — not just how much iron is in your blood right now, but how much your body has in reserve. It’s the single most common nutritional driver of hair shedding I see in practice.

The standard reference range often starts as low as 12 or 15 and goes up to around 150. So when a result comes back at 20 or 30, it looks perfectly acceptable on paper. But research consistently shows that hair needs ferritin above 50 to grow optimally, and many trichologists — myself included — prefer to see it closer to 70 or above.

If your ferritin is below 50 and you’re shedding, this is the first place to start. Iron supplementation needs to be done carefully, ideally with professional guidance, because the form, dose, and timing all matter — and taking too much has its own problems. But when it’s addressed properly, the difference can be significant.

One thing worth knowing: ferritin rises slowly. Even with good supplementation, it can take three to six months to build your stores to a level that supports regrowth. This is why I always encourage people to check early rather than waiting — the sooner you know, the sooner recovery begins.

Vitamin D

Vitamin D plays a role in the hair growth cycle that’s often underestimated. Low levels are associated with increased shedding and may affect the follicle’s ability to cycle properly. In the UK and Ireland, deficiency is remarkably common — particularly through autumn and winter months when sunlight exposure drops.

The reference range typically starts around 25 nmol/L, but for optimal health and hair, most practitioners recommend 75 nmol/L or above. I regularly see clients whose vitamin D is in the 30s or 40s — technically within range, officially insufficient for what their hair needs.

Supplementation is straightforward and affordable. A daily vitamin D3 supplement, ideally taken with a meal containing some fat for better absorption, is usually all it takes. But you need to know your starting level to get the dose right.

Zinc

Zinc is essential for cell division — and since hair follicles are some of the fastest-dividing cells in the body, they’re particularly sensitive to low zinc. Deficiency can contribute to shedding, thinning, and changes in hair texture.

Zinc is particularly worth checking if you’ve had a period of reduced appetite or restricted eating — which is exactly what happens on GLP-1 medications, crash diets, or during periods of high stress when eating falls down the priority list.

Like ferritin, zinc can sit within the “normal” range and still be suboptimal for hair. And supplementation needs balance — too much zinc can deplete copper, so it’s best guided by your actual levels rather than guesswork.

Thyroid function (TSH, T3, T4)

Thyroid hormones regulate metabolism across your entire body, including your hair follicles. Both an underactive thyroid (hypothyroidism) and an overactive thyroid (hyperthyroidism) can cause diffuse hair shedding that looks very similar to telogen effluvium.

I always recommend a full thyroid panel — TSH alone doesn’t give the complete picture. T3 and T4 show how much active thyroid hormone your body is actually producing and using. Some people have a TSH that looks “normal” while their T3 or T4 tells a different story.

Thyroid issues are also more common in women, particularly around perimenopause and menopause, which means thyroid-related shedding can easily be misattributed to “just hormones” or “just ageing” if the right tests aren’t done.

Vitamin B12 and folate

B12 and folate both play roles in red blood cell formation and oxygen delivery — which means they indirectly support the blood supply to your follicles. Low levels can contribute to shedding, fatigue, and brittle hair.

Vegetarians, vegans, and anyone on long-term medication that affects gut absorption should be especially mindful of B12 levels. And folate — particularly if you have a genetic variant like MTHFR that affects how you process it — may need to be taken in its methylated form to be properly used by your body. This is one of the things we can identify through genetic testing, and it’s a detail that often makes the difference between a supplement working and not working.

The tests I check alongside blood work

Blood work gives us the nutritional picture. But when I’m assessing a client’s hair properly, I also look at two other things:

Scalp health. A trichoscopy examination lets me look at the scalp under magnification to assess follicle density, miniaturisation, scalp condition, and the ratio of growing to resting hairs. This tells me whether what you’re experiencing is purely telogen effluvium or whether there’s something else going on — like early pattern thinning or an inflammatory scalp condition — that blood work alone wouldn’t catch.

Genetic factors. Our Fagron TrichoTest looks at specific genetic markers that affect how your body processes nutrients, how sensitive your follicles are to DHT, and how you respond to certain treatments. For example, if you carry variants that affect iron absorption or vitamin D metabolism, that changes both the supplementation approach and the expected timeline. It’s a layer of personalisation that makes everything else more effective.

What to do with your results

Getting the tests done is step one. Knowing what the numbers mean for your hair — not just whether they’re “in range” — is where the real value lies.

If you’re comfortable interpreting results yourself, here’s a quick reference:

Ferritin: Aim for 50+ (ideally 70+) for hair. Below 50 with shedding = almost certainly a contributing factor.

Vitamin D: Aim for 75+ nmol/L. Below 50 = likely affecting your hair cycle.

Zinc: Mid-range or above on your lab’s reference range. Low-normal with shedding = worth addressing.

TSH: Within range, but check T3 and T4 too. Borderline results warrant closer attention.

B12: Above 300 pg/mL ideally. Below 200 = deficient.

If you’d rather have someone look at the full picture with you, that’s exactly what a consultation is for. I look at blood work alongside your clinical history, scalp assessment, and — where relevant — genetic markers, and we build a clear, personalised plan from there. It takes the guesswork out of it completely.

One thing I’d really encourage

If you’re experiencing shedding — whether it’s related to GLP-1 medication, postpartum changes, stress, menopause, or anything else — don’t wait months hoping it resolves before getting your levels checked. Blood work is one of the simplest, most affordable, and most revealing things you can do, and the earlier you do it, the more time you save.

I’ve had clients who spent a year trying different shampoos and supplements before anyone thought to check their ferritin. When we did, it was 18. That’s not a shampoo problem. That’s a ferritin problem. And it could have been addressed twelve months earlier.

Your hair is giving you information. Blood work helps you read it.

Not sure what to ask for?

Drop us a Private Note and I’ll send you a straightforward list of exactly what to request from your GP — tailored to your situation. If you’ve already had blood work done and aren’t sure what the results mean, send those through too. I’m happy to take a look.

 

[Reserve your Hair Health Plan →]

 

This is part of our Hair Health series on Studio Notes. If you’re shedding after starting a GLP-1 medication, our guide to Ozempic, Wegovy & Mounjaro hair shedding covers why it happens and what helps, and our GLP-1 shedding timeline walks through the month-by-month pattern.

If you’re not sure whether you’re shedding or experiencing breakage, our 30-second check will help you tell the difference.

 

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Hair Health Essentials combines genetic testing, blood biomarker analysis, and personalised treatment protocols with naturally formulated, COSMOS-certified products — because your hair deserves both the science and the care. Clinics at Harley Street London, Blackrock Dublin, and Eden One Health Club Dublin.

This article is for information purposes and doesn’t replace medical advice. Please discuss any test results or supplementation with a qualified practitioner.