Vitamins & Minerals
Normal Serum Iron Levels: Reading a UK Number
Reviewed by a qualified clinician · analysed at UKAS-accredited UK labs (ISO 15189)
Last reviewed September 20266 min read
Every Helvy guide is written by our health editors, then checked by a qualified clinician before it goes live and re-checked as the science moves. We name clinical roles, not individuals, until each reviewer has agreed to be credited publicly. This is wellness guidance to help you understand your own data, not a diagnosis.
QUICK ANSWER
UK labs report serum iron in micromoles per litre. North West London Pathology reads 12 to 31 umol/L in adult men and 9 to 30 in adult women. Newcastle publishes a single adult range of 6 to 35. The number swings with the time of day and with what you last ate, so it is read alongside ferritin rather than on its own.
Not sure which markers you need? Build your test →Your serum iron comes back at 8. The range on the report starts at 9. You are one point under, and the internet is already telling you that you are anaemic.
Hold on. Serum iron is the most volatile number on an iron panel. It moves with breakfast, with the time of the draw, and with whether you took a supplement that morning. This guide covers the UK ranges, why two NHS labs can disagree by so much, and which numbers actually answer the question you came here with. If your report lists all five markers, start with how an iron studies panel is read as a set.
1. What is a normal serum iron level in the UK?
Serum iron is the iron travelling in your blood right now. UK labs report it in micromoles per litre, written umol/L. Here is what two NHS services publish.
If you came looking for an age chart, iron levels by age explains why UK labs do not print one.
| Lab | Men | Women |
|---|---|---|
| North West London | 12 to 31 | 9 to 30 |
| Newcastle Hospitals | 6 to 35 (16 and over) | 6 to 35 (16 and over) |
Look at the bottom ends. A result of 8 umol/L is below range in North West London and comfortably inside range in Newcastle. Nothing about the blood changed. Only the lab did. Newcastle Hospitals Laboratories also splits out children, reading 7 to 22 umol/L up to age 16.
So read your number against the range printed on your own report. That is the only range that was used to produce it.
2. Why the same person gets a different number each time
Because serum iron is a snapshot of traffic, not of storage. Newcastle puts it plainly: serum iron levels can have substantial day-to-day fluctuations.
Three things move it, and all three are ordinary.
- The clock. Serum iron tends to run higher in the morning and lower later in the day.
- Your last meal. A meal with iron in it lifts the reading for hours.
- Supplements. An iron tablet can send the number up sharply on the day you take it.
There is a fourth if you have periods. Serum iron reads lowest during menstruation and climbs across the rest of the month. Ferritin barely moves, which is part of why it is the better number to compare. If your periods are heavy, the test your GP is told to run leaves ferritin out. Absorption is a separate question, and the vitamin C answer is not the one most people expect.
That is why a single serum iron result is weak evidence on its own. Take the same blood twice on two ordinary days and the two numbers can land on opposite sides of the range.
3. What serum iron actually measures
Two words worth separating, because most confusion about iron sits between them.
Serum iron is the iron currently riding around your bloodstream on a carrier protein. Think of it as the vans on the road this morning.
Ferritin is the protein that holds iron in reserve, so it shows how much iron you have banked. Think of it as the warehouse.
You can have a busy road and an empty warehouse. That is exactly why a normal serum iron does not rule out low stores, and why a low one does not prove them.
Serum iron swings a lot through the day. Read against your TIBC, it becomes a saturation figure that holds much steadier.
4. The numbers that read your iron properly
NHS Highland is blunt about where serum iron sits in the pecking order.
“The serum iron is not a good test for iron deficiency as it varies depending on time of day, recent meals and does not reflect iron stores.”
— NHS Highland, iron deficiency guidelines
The same guideline puts ferritin first. It says a ferritin under 30 micrograms per litre has 92% sensitivity and 98% specificity for iron deficiency, and that in the vast majority of cases a ferritin is all that is required.
Two more markers finish the picture, and both are calculated rather than measured directly.
- Transferrin is the carrier protein iron travels on. Newcastle reads 2.0 to 3.6 g/L in anyone over four weeks old.
- TIBC, or total iron binding capacity, describes how much room there is on those carriers.
- Transferrin saturation is the share of that room being used. Newcastle calculates it as iron in umol/L multiplied by 3.98, divided by transferrin in g/L.
Saturation is the useful one, because it puts your serum iron in context instead of leaving it floating. Our normal transferrin saturation levels guide reads that percentage in detail, and the saturation calculator works it out from your own two numbers.
5. Which blood test reports your serum iron
The marker is iron, reported in umol/L. Helvy's Vitamins & Minerals panel (£159) reports it alongside ferritin, transferrin, transferrin saturation, TIBC, vitamin B12, folate, vitamin D and magnesium. The whole reason the full set is in there is that serum iron on its own answers very little. The same is true of folate, and normal folate levels sets out the range it is read against.
One honest boundary. Vitamins & Minerals is the only Helvy panel that carries iron markers, so it is the one to check if iron is specifically what you want measured. It is also not a full anaemia screen, because that needs a full blood count and a clinical judgement as well.
Take a morning sample and leave that day's iron supplement off, or the reading will not reflect your usual level. If you have been taking iron for months without feeling better, iron tablets not working covers what people usually find. The build-my-test tool helps you pick markers.
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See your serum iron next to the markers that explain it
Helvy's home blood tests report iron in UK units with plain-English context, read beside ferritin and transferrin saturation rather than on its own. Samples are processed by UKAS-accredited UK labs.
Frequently asked questions
What is a normal serum iron level in umol/L?
North West London Pathology reads 12 to 31 umol/L in adult men and 9 to 30 in adult women. Newcastle Hospitals publishes 6 to 35 for anyone aged 16 and over. Use the range printed on your own report.
Is a serum iron of 8 umol/L low?
It sits below the North West London range for both sexes and inside the Newcastle range. That spread is exactly why one serum iron reading rarely settles anything, and why ferritin is the test NHS Highland puts first.
Does eating before the test change serum iron?
Yes. NHS Highland names recent meals and the time of day as two reasons serum iron is a poor standalone test for iron deficiency. Newcastle notes substantial day-to-day fluctuations in the same marker.
What is the difference between serum iron and ferritin?
Serum iron is the iron moving through your blood at the moment of the draw. Ferritin is the protein that holds iron in reserve, so it reflects stores. A normal serum iron does not tell you the stores are full.
How is transferrin saturation worked out?
Newcastle Hospitals publishes the formula as iron in umol/L multiplied by 3.98, divided by transferrin in g/L. It gives the share of your carrier proteins that are carrying iron, which puts a serum iron number in context.
Should I stop my iron supplement before testing?
Leave that day's dose off and sample in the morning, otherwise the reading reflects the tablet rather than your usual level. If you take iron on prescription, check with a qualified clinician before changing anything.
Related guides
Ferritin Blood Test UK
The marker NHS Highland puts first for iron.
Normal Transferrin Saturation Levels UK
The percentage that puts your serum iron in context.
Iron Deficiency Blood Test
Ferritin, iron studies and what your results mean.
Optimal Ferritin Levels UK
Where the range ends and where people feel better.
Full Blood Count UK
The other half of an anaemia assessment.
Blood Test Reference Ranges UK
Why normal on a lab report is a population range, not a target.