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Restless Legs Blood Test UK: Why Ferritin Is the First Thing to Check
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The single most useful blood test for restless legs syndrome is ferritin, the marker of iron stores. Low iron in the brain is one of the best-understood drivers of restless legs, and crucially the target ferritin here is higher than the usual lab cut-off — treatment is often considered when ferritin is below about 75 µg/L, not just when it is flagged as low. Kidney function, thyroid, B12 and blood sugar are checked alongside.
Restless legs syndrome — the irresistible urge to move the legs, usually worse in the evening and at rest — can be miserable, and it quietly wrecks sleep. The good news is that it has one standout checkable cause, and it is one a routine test often misses by reading the result against the wrong threshold.
That cause is iron. Not necessarily iron-deficiency anaemia — the haemoglobin can be perfectly normal — but low iron stores, which affect the brain's dopamine system in a way that drives the restless sensation.
This guide explains why ferritin matters most, the higher target that applies, and the other blood tests worth running alongside it.
1. Ferritin: the first test
Ferritin is the protein that stores iron, and its blood level is the best everyday measure of how much iron you have in reserve. In restless legs, low iron in the brain interferes with dopamine signalling, the system that controls movement, and that is thought to produce the characteristic urge to move.
Because of that link, checking ferritin is the standard first step when restless legs is being assessed, and topping up iron when stores are low is one of the few treatments that addresses a cause rather than just the symptom. The iron deficiency blood test guide covers ferritin and the wider iron studies in full.
2. Why the target is higher
Here is the detail that catches people out. A standard lab might flag ferritin as low only below around 15 to 30 µg/L. For restless legs, that threshold is too low: the evidence supports considering iron treatment when ferritin is below about 75 µg/L, because the brain seems to need more generous stores than the rest of the body to keep the symptom at bay.
So a ferritin result reported as “normal” can still be low enough to matter for restless legs. That is why the number, not just the in-range flag, is worth seeing — and why this is a useful thing to discuss specifically with a clinician familiar with restless legs.
3. Why anaemia can be normal
Restless legs is driven by low iron stores, which is different from anaemia. Anaemia means there are too few red blood cells or too little haemoglobin; iron stores can run low well before that happens. So someone with restless legs can have a completely normal full blood count and haemoglobin while their ferritin tells a different story.
This is exactly why ferritin is the test to ask about. A normal blood count is reassuring about anaemia but says little about the iron stores that matter here.
4. The other causes to rule out
Iron is the headline, but restless legs is associated with a few other conditions a blood test can help check:
- Kidney disease, which is strongly associated with restless legs.
- Diabetes and the nerve effects of high blood sugar.
- An underactive thyroid, and low vitamin B12 or folate.
- Pregnancy, a common and usually temporary trigger.
Some medications can also bring restless legs on or make it worse, which is a conversation for a clinician rather than a blood test.
5. Which blood tests to consider
For restless legs, the commonly considered panel is:
- Ferritin (and transferrin saturation) — the priority, read against the higher target.
- Kidney function — creatinine and eGFR.
- HbA1c — for diabetes.
- Thyroid function, vitamin B12 and folate.
- A full blood count for the wider picture.
Read together, these cover the main checkable contributors, with ferritin doing most of the work.
6. NHS and private testing
A GP assessing restless legs will usually check ferritin and a few related markers, and NICE guidance specifically highlights iron stores as worth correcting. If your ferritin has been called normal but sits below that higher restless-legs target, it is worth raising the specific number with your clinician.
Private testing can give you the exact ferritin figure and a fuller panel to bring to that conversation, which is helpful precisely because the interpretation here hinges on a number rather than an in-range flag. It complements a clinical assessment rather than replacing it.
7. Frequently asked questions
What blood test is done for restless legs?
Ferritin is the key test, because low iron stores are a leading cause of restless legs. Kidney function, HbA1c, thyroid, B12 and folate are usually checked alongside. Ferritin matters most and is read against a higher target than usual.
What ferritin level causes restless legs?
For restless legs, iron treatment is often considered when ferritin is below about 75 µg/L — higher than the usual low-ferritin cut-off — because the brain appears to need more generous iron stores to keep symptoms at bay. A “normal” ferritin can still be low enough to matter.
Can I have restless legs with a normal blood count?
Yes. Restless legs is driven by low iron stores, not anaemia, so the full blood count and haemoglobin can be normal while ferritin is low. That is why ferritin specifically is the test to ask about.
Does low iron cause restless legs?
Low iron in the brain interferes with the dopamine system that controls movement, and it is one of the best-understood drivers of restless legs. Correcting low iron stores is one of the few treatments that addresses a cause rather than just the symptom.
Should I see my GP or test privately?
See your GP, who can check ferritin and the related markers and advise on treatment. Private testing can give you the precise ferritin number and a fuller panel to bring along, which is useful because the decision hinges on the exact figure.
CHECK YOUR IRON STORES
See your exact ferritin number, not just a flag.
A Helvy panel can set ferritin alongside a full blood count, kidney, thyroid and B12 in one home finger-prick kit — so you can read ferritin against the higher restless-legs target. Results in 5 working days, analysed at UKAS-accredited UK laboratories, with qualified clinician review.
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