The Blood Test Your GP Never Ordered
Written by the Fix My Hair Editorial Team · Clinician-reviewed by Dr Hisham Band · GMC No. 7550130 · Last reviewed 28 Jan 2026There’s a good chance your GP has never checked the one blood marker most likely to be causing your hair loss. It’s not because they don’t care — it’s because the reference range they use isn’t designed with hair health in mind.
Why ferritin is the most commonly missed cause
Ferritin is your body’s iron store, and one of the strongest nutritional drivers of hair growth. Low ferritin is the single most common cause we identify — and the one most often overlooked.
The difference between ferritin and haemoglobin
A GP usually checks haemoglobin to rule out anaemia. You can have perfectly normal haemoglobin and still have a ferritin level far too low for healthy hair. They are not the same test — and the one that matters for hair often is not run.
The other six markers and what they reveal
Alongside ferritin we measure DHT, thyroid function, testosterone, vitamin D, a full blood count and liver function. Together they explain why hair is being lost and whether medication is safe to start.
Why we test all seven before recommending treatment
Treating the wrong cause never works. Diffuse loss driven by thyroid or iron will not respond to a DHT blocker. Testing first means the plan is built on your actual biology, not a guess.
What a normal result means vs an optimal one
“Normal” on a GP report means “not clinically deficient.” Optimal for hair health is a higher bar — a ferritin sitting in the normal range can still be holding your hair back.
How to get tested — three options
An at-home finger-prick kit, a free in-clinic venous draw, or included free with a hair transplant. All three include the same lab analysis and a plain-language specialist report.
Why standard care misses it
If you’ve asked your GP about hair loss, you may have been told your bloods are “normal” — or not offered a test at all. That’s not negligence; it’s the system. NHS appointments are short, hair loss is rarely treated as urgent, and the standard panels GPs order are designed to catch disease like anaemia, not to optimise hair growth. A ferritin level that’s fine for preventing anaemia can still be far too low for healthy hair — and it won’t be flagged, because by the lab’s reference range it’s “in range.”
The reference-range problem
Lab reference ranges represent the spread of the general population, not the level that’s optimal for a demanding tissue like the hair follicle. A result can sit at the bottom of “normal” and still be holding your hair back. A test interpreted with hair in mind reads those numbers differently — looking for the optimal level, not merely the absence of disease. We unpack this in your blood test results explained.
The questions worth asking
Whatever route you take, the useful questions are: was ferritin actually measured (not just haemoglobin)? Were thyroid, vitamin D, B12 and zinc included? And were the results read against optimal levels for hair, or just the standard range? If the answer is no, an important piece of the picture may be missing — which is the whole reason we test before we treat.
Common questions
Can my GP order these tests? Sometimes, but they may decline if your levels are “normal” or hair loss isn’t deemed clinical — and they may not interpret them for hair. A dedicated hair-health panel is built for exactly this.
Is it worth testing if I’ve been told I’m fine? Often yes — “fine” usually means “not anaemic,” which isn’t the same as optimal for hair.
Key takeaways
- Ferritin below 70 μg/L impairs growth even with normal haemoglobin
- Standard GP reference ranges are not optimised for hair health
- Thyroid dysfunction causes diffuse loss that is frequently misdiagnosed
- DHT levels determine the appropriate treatment approach
- In-clinic testing at Fix My Hair is free
