Serum Iron
Serum iron is the iron currently on its way through your blood, bound to its transport protein. It is a snapshot that sits highest in the morning and shoots up after an iron tablet or a piece of meat; on its own it says little, as the building block of transferrin saturation a lot.
Serum Iron reference ranges
What does your value mean?
Normal: women 10.7 to 25.0, men 14 to 30 µmol/L
Enter your value as it appears on your results. Range for adults.
Serum Iron high or low: what it means
Serum Iron too low
Belongs with: Iron deficiency
Little iron in transit, from a deficiency or because the body locks it away.
| Cause | How often |
|---|---|
| The body locks iron away in the store to deny bacteria any; serum iron falls while ferritin actually rises, and CRP shows it | Often |
| Serum iron sits highest in the morning and falls over the day by a third or more; an afternoon value looks wrongly low | Often |
| The store is empty and little more passes by; ferritin is then low as well and transferrin high | Often |
| Heavy periods, or unnoticed from stomach or gut; the iron that was in transit leaves with the blood | Often |
Serum Iron too high
Usually iron that just came in, and rarely iron that cannot get out.
| Cause | How often |
|---|---|
| An 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 |
| Iron from meat is absorbed fast and shows in your blood within hours; that is why you have blood drawn fasting | Sometimes |
| A damaged liver releases stored iron into the blood; the liver values are then abnormal too | Sometimes |
| In haemochromatosis the gut absorbs too much iron; serum iron and saturation are high and ferritin slowly rises | Rare |
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. 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.
How does a serum Iron blood test work?
- Which test. Serum Iron is in the Iron & fatigue test (€99) and in .
- Fasting. Every draw is fasted: nothing to eat or drink from midnight, only water. Appointments are therefore in the morning, until 12:00.For serum iron it matters too: fasting in the morning the value is highest and least disturbed by food. Skip an iron tablet the day before and that morning.
- Referral. Not needed. Serum iron is in the iron profile you can have measured yourself, together with ferritin and transferrin.
- 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.
- Where to draw. You can draw at 400+ locations near you, no referral needed. See the locations
More about serum Iron
Serum Iron explained
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.
How do you read serum Iron?
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. 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.
Frequently asked questions
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.
Related biomarkers
Read on
Sources 5
- 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
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Educational information only, not medical advice. Consult a healthcare professional for clinical decisions.
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