What is serum Iron?
Of all the iron in your body, most sits in your red blood cells and in your store, ferritin. A small part is in transit: from the gut to the bone marrow, from the spleen where old cells are broken down back to production. That iron in transit travels bound to transferrin, the transport protein, and serum iron measures how much of it is in your blood right now. It is therefore the most mobile of all the iron values. It sits highest in the morning and falls over the day by a third or more. It rises within hours of an iron tablet or a meat meal. And it falls with an inflammation, because your body then locks iron away in the store to deny bacteria any. A single loose number therefore says little about your iron status; ferritin says how much you have in stock, and serum iron how much happens to be passing by now. Your report shows serum iron in µmol/L. Normal is about 14 to 30 µmol/L for a man up to 80 years and 10.7 to 25 µmol/L for a woman, fasting and drawn in the morning. Its real value lies in the division by transferrin: that gives transferrin saturation, the percentage of taxis that is occupied, and that is the measure of how much iron is available right now.
Why is serum Iron relevant?
Serum iron is rarely the value you read something from, but it is the value you need. Without serum iron there is no transferrin saturation, and saturation is the best measure of how much iron your cells can take right now. Ferritin says how full the warehouse is; saturation says whether it is delivering. In an iron deficiency both are low, in iron overload saturation is high first, and in an inflammation ferritin is high while saturation is low. In that last combination lies the strength: an inflammation hides a deficiency in the ferritin, and serum iron and saturation show it anyway. For anyone who does sport there is a second reason. With hard training and in the days after, the body sits slightly in inflammation mode, and serum iron then falls temporarily while the store is still normal. A falling serum iron with a falling saturation in an athlete with a still normal ferritin is an early sign that the supply is not keeping up with the demand. If you have blood drawn on a rest day in the morning, you compare fairly. The high side usually comes from outside: an iron tablet or an iron-rich meal in the hours before the draw lifts serum iron sharply and has nothing to do with your iron status. A high serum iron with a high saturation, fasting and without a supplement, is the first sign of iron overload, and that is a reason to read ferritin alongside.
Serum Iron reference ranges
What counts beside the number:
- What time you had blood drawn, and whether you were fasting
- Whether you took an iron tablet or a multivitamin with iron in the days before
- Ferritin, because that says whether the store is empty or locked
- CRP, because an inflammation pushes serum iron down without a deficiency
- Transferrin and saturation, where serum iron gains its meaning
- Whether you trained hard or were ill in the days before
The bands above apply to a fasting morning draw, and for serum iron that is no detail: the value falls over the day by a third or more, rises within hours of an iron tablet or a meat meal and falls with every inflammation. The labs also differ here more than for most values. So never read serum iron alone, but beside ferritin, transferrin, transferrin saturation and CRP.
What Dutch labs actually use
10.7 – 25µmol/L
Between 7 and 10.7 and between 25 and 35 it depends on the lab, because each sets its limits on its own method and population. Above 35 every lab calls it abnormal.
every lab calls 10.7 – 25 µmol/L normal. Between 7 and 10.7 and between 25 and 35 it depends on the lab.
Every age, per lab
| Laboratory | Group | Reference range |
|---|---|---|
| Unilabs(Saltro, Medlon, SHO, Atalmedial)2026 | Under 30 days | 17–40 µmol/L |
| Men | 14–35 µmol/L | |
| Women | 10–25 µmol/L | |
| Star-shl2026 | Men 19–50 yrs | 8–39 µmol/L |
| Women 19–50 yrs | 7–35 µmol/L | |
| Men 51–65 yrs | 8–35 µmol/L | |
| Women 51–65 yrs | 8–30 µmol/L | |
| Men 66–80 yrs | 7–31 µmol/L | |
| Women 66–80 yrs | 8–30 µmol/L | |
| Men 81+ | 8–29 µmol/L | |
| Women 81+ | 7–28 µmol/L | |
| Men 13–18 yrs | 9–35 µmol/L | |
| Women 13–18 yrs | 6–35 µmol/L | |
| Certe2026 | All ages | 10–30 µmol/L |
| Clinical Diagnostics2026 | Infant | 7.2–17.9 µmol/L |
| Child | 9.0–21.5 µmol/L | |
| Men | 12.5–32.2 µmol/L | |
| Women | 10.7–32.2 µmol/L |
Each band as the lab publishes it, retrieved in 2026, unless marked otherwise.
Serum Iron high or low: what it means
A low serum iron means little iron is in transit right now, and that has two very different reasons. The most common explanation first: an inflammation or infection locking the iron away, drawn in the afternoon or after hard training, a real iron deficiency, and blood loss. You tell the difference with ferritin and CRP: low serum iron with low ferritin is a deficiency; low serum iron with high ferritin and high CRP is an inflammation, and then the store is not empty but locked. A high serum iron is usually from outside: an iron tablet or a meat meal in the hours before. Drawn fasting and without a supplement, a high serum iron with a saturation above 45% points at iron overload or at a liver releasing its iron; ferritin and the liver values say which of the two. What you do about it: with a real deficiency you refill the store, with red meat, fish, legumes and green vegetables with vitamin C alongside, and where needed an iron tablet every other day. With a low serum iron from inflammation you do nothing about the iron and everything about the inflammation. With a high serum iron from a supplement you simply have blood drawn once more, fasting and without the tablet. Never read serum iron alone, but always beside ferritin, transferrin, transferrin saturation and CRP. Have blood drawn in the morning, fasting, on a rest day, and keep to the same time when comparing.
What lowers it
Little iron in transit, from a deficiency or because the body locks it away.
| Cause | How often |
|---|---|
| Inflammation or infectionThe body locks iron away in the store to deny bacteria any; serum iron falls while ferritin actually rises, and CRP shows it | Often |
| Drawn in the afternoonSerum iron sits highest in the morning and falls over the day by a third or more; an afternoon value looks wrongly low | Often |
| Real iron deficiencyThe store is empty and little more passes by; ferritin is then low as well and transferrin high | Often |
| Blood lossHeavy periods, or unnoticed from stomach or gut; the iron that was in transit leaves with the blood | Often |
What raises it
Usually iron that just came in, and rarely iron that cannot get out.
| Cause | How often |
|---|---|
| Iron supplementsAn iron tablet in the hours before the draw lifts serum iron sharply; skip it that day if you want to know your own value | Often |
| Just after a meat mealIron from meat is absorbed fast and shows in your blood within hours; that is why you have blood drawn fasting | Sometimes |
| Liver damageA damaged liver releases stored iron into the blood; the liver values are then abnormal too | Sometimes |
| Iron overloadIn haemochromatosis the gut absorbs too much iron; serum iron and saturation are high and ferritin slowly rises | Rare |
How does a serum Iron blood test work?
- Referral
- Not needed. Serum iron is in the iron profile you can have measured yourself, together with ferritin and transferrin.
- Fasting
- Yes, and in the morning, because the value is highest then and least disturbed by food. Skip an iron tablet the day before and that morning.
- When
- On a rest day and not during or just after an infection, because hard training and inflammation push serum iron down temporarily.
- The draw
- One tube of blood from a vein in your arm. Ferritin, transferrin and CRP come from the same draw, and saturation is calculated from it.
- Repeating
- With an abnormal value first once more fasting and in the morning; beyond that together with ferritin, three months after starting iron.
- Which test
- Serum Iron is in the Iron & fatigue test (€99) and in .
- Where to draw
- You can draw at 250+ locations near you, no referral needed. See the locations
Frequently asked questions
What is serum iron?
The iron currently on its way through your blood, bound to transferrin, the transport protein. That is only a fraction of all your iron; most sits in your red blood cells and in your store, ferritin. Serum iron therefore does not say how much iron you have, but how much is passing by now, and that swings strongly over the day.
What is a normal serum iron level?
About 14 to 30 µmol/L for a man up to 80 years and 10.7 to 25 µmol/L for a woman, where the labs overlap, drawn fasting and in the morning. Later in the day or after a meal those figures no longer apply. More important than the band is the combination with ferritin and transferrin saturation.
What does a low serum iron mean?
That little iron is in transit right now, and that has two very different reasons. With a real deficiency the store is empty: ferritin is then low as well and transferrin actually high. With an inflammation or infection your body locks iron away in the store: ferritin is then high and so is CRP, and the store is not empty but locked. Drawing in the afternoon or after hard training also pushes the value down without anything being wrong.
What does a high serum iron mean?
Usually iron that just came in: an iron tablet or a meat meal in the hours before the draw. Have blood drawn once more, fasting and without a supplement. If the value stays high and transferrin saturation is above 45%, that points at iron overload or at a liver releasing stored iron; ferritin and the liver values say which of the two.
Why does serum iron swing so much?
Because it measures what happens to be passing by. The value follows a daily rhythm with a peak in the morning and falls over the day by a third or more. Food with iron, and certainly an iron tablet, lifts it within hours. And with every inflammation, including the mild one after hard training, your body locks iron away and the value falls. So always have blood drawn in the morning, fasting and on a rest day, and only compare measurements from the same time.
What does serum iron have to do with transferrin saturation?
Everything: saturation is serum iron divided by transferrin, the percentage of taxis that is occupied. That number says how much iron is available for your cells right now, and it is the value where serum iron gains its meaning. Low in a deficiency, high in overload, and in an inflammation low while ferritin is high, which lets it show a deficiency that ferritin hides.
Can I raise my serum iron myself?
With a real deficiency yes, by filling the store: red meat, fish, poultry, legumes and green vegetables with vitamin C alongside, and where needed an iron tablet every other day. Serum iron then rises quickly, ferritin only after months. If the low value is the result of an inflammation, iron does not help and removing the inflammation does.
Do I need to fast for a serum iron test?
Yes, and have blood drawn in the morning. Skip an iron tablet the day before and that morning, and choose a rest day, because hard training pushes the value down. Ferritin, transferrin and CRP come from the same draw, and without those three serum iron cannot be read.
Which tests include serum Iron?
Serum Iron is in the Iron & fatigue test (€99, also as an add-on for €15) and in .
Related biomarkers
Read on
Sources
- 1.Unilabs, test catalogue (Dutch): iron. 2026. bepalingenklapper.nl
- 2.Star-shl, test catalogue (Dutch): iron. 2026. star-shl.nl
- 3.Certe, test catalogue (Dutch): iron. 2026. bepalingenwijzer.certe.nl
- 4.Clinical Diagnostics, lab guide (Dutch): iron. 2026. clinicaldiagnostics.nl
- 5.LESA Laboratory diagnostics (Dutch primary-care laboratory agreement). 2026. richtlijnen.nhg.org
Educational information only, not medical advice. Consult a healthcare professional for clinical decisions.
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