What is transferrin Saturation?
Iron travels through your blood in transferrin, the transport protein that can carry two iron atoms per molecule. Transferrin saturation is the percentage of those seats that is occupied right now: serum iron divided by the transport capacity. At a third occupied, plenty of iron is circulating for the marrow; at a sixth there is too little; at more than half the transport is full and free iron starts reaching tissue where it does not belong. That makes saturation a different question from ferritin. Ferritin says how full the warehouse is; saturation says whether it is delivering. Usually they run in step, but exactly where they diverge sits the information. With an inflammation your body locks iron away in the store: ferritin rises, saturation falls, and the deficiency that ferritin hides, saturation shows. In iron overload saturation rises first, years before ferritin becomes high and before there is damage. Your report shows saturation in percent. Normal is about 20 to 43% for a fasting morning draw, where the labs overlap; below 20% an iron deficiency is likely, above 45% fits overload. Because the value is calculated from serum iron, it swings with it over the day: highest in the morning, and after an iron tablet or a meat meal temporarily much higher.
Why is transferrin Saturation relevant?
The first reason to know your saturation is that it sees what ferritin misses. Anyone regularly inflamed, through sport, a chronic condition, excess weight or simply a cold in the week of the draw, has a ferritin that looks too good. Saturation then actually falls, and a low saturation beside a normal or high ferritin is the picture of an iron deficiency hiding behind inflammation. For athletes that is the ordinary situation: after hard training the body sits slightly in inflammation mode for days, and saturation is then the most honest of the iron values, provided you have blood drawn on a rest day in the morning. The second reason is the other side, and it is more important than it seems. Inherited iron overload, haemochromatosis, occurs in the Netherlands in about one in two hundred people of Northern European descent and often goes unnoticed for decades, because the symptoms are vague: tiredness, joint pain, abdominal complaints, less desire. Meanwhile the iron builds up in liver, heart, pancreas and joints. Saturation is the earliest value that gives it away, well before ferritin sits high, and the treatment is simple and complete: giving blood regularly. A persistent saturation above 45%, fasting and without a supplement, is therefore the one iron value on which you do not wait. The third reason is that saturation shows whether topping up works. After starting iron, saturation rises within days, long before ferritin moves; if it stays low, the iron is not being absorbed, and that is a clue that it lies with the gut or with an inflammation.
Transferrin Saturation reference ranges
What counts beside the number:
- Ferritin: low saturation with low ferritin is an empty store, with high ferritin a store on lock
- CRP, because inflammation pushes saturation down without a deficiency
- What time you had blood drawn, whether you were fasting and whether you took an iron tablet
- Serum iron and transferrin, which saturation is calculated from
- With a high value: your liver values, and whether iron overload runs in the family
- Whether you trained hard or were ill in the days before
The band applies to a fasting morning draw: saturation follows serum iron, which falls over the day and rises after an iron tablet or a meat meal. Not every lab prints a band, because it is a calculated value. More important than the band are the two limits: below 20% too little iron is available, above 45% the transport is full, and the latter is the earliest clue to iron overload. Always read saturation beside ferritin and CRP.
What Dutch labs actually use
20 – 43%
Between 6 and 20 and between 43 and 45 it depends on the lab, because each sets its limits on its own method and population. Above 45 every lab calls it abnormal.
every lab calls 20 – 43 % normal. Between 6 and 20 and between 43 and 45 it depends on the lab.
Every age, per lab
| Laboratory | Group | Reference range |
|---|---|---|
| Unilabs(Saltro, Medlon, SHO, Atalmedial)2026 | Men | 12–43 %converted |
| Women | 6–43 %converted | |
| Certe2026 | All ages | 20–45 % |
| Clinical Diagnostics2026 | Adults | 20–45 % |
Each band as the lab publishes it, retrieved in 2026, unless marked otherwise.
Transferrin Saturation high or low: what it means
A low saturation means too little iron is available right now. From common to rare: an iron deficiency, an inflammation locking the iron away, drawn in the afternoon or after hard training, and a pregnancy, in which the transport grows and the baby asks for iron. Ferritin and CRP tell the difference: low saturation with low ferritin is an empty store, low saturation with high ferritin and high CRP is a store on lock. A high saturation is usually an iron tablet or an iron-rich meal in the hours before the draw, and that is settled with a fasting repeat. Fasting and without a supplement, and persistently above 45%, it is iron overload or a liver releasing its iron; ferritin and the liver values say which, and with overload investigation for haemochromatosis belongs, in family members too. What you do about it: with a deficiency you refill the store with red meat, fish, legumes and green vegetables with vitamin C, and where needed an iron tablet every other day; saturation shows within days whether it is working. With a low saturation from inflammation you do nothing about the iron. With overload the treatment is giving blood, and it helps not to take a vitamin C supplement with meals and not to take an iron-containing multivitamin. Set saturation beside ferritin and CRP, and beyond that beside serum iron and transferrin, which it is calculated from. Have blood drawn in the morning, fasting, on a rest day, and only compare morning values with each other.
What lowers it
Too little iron on the taxis, from a deficiency or because the body locks it away.
| Cause | How often |
|---|---|
| Iron deficiencyThe store is empty and little more passes by, while the liver actually sends more taxis; ferritin is then low too | Often |
| InflammationThe body locks iron away in the store; saturation falls while ferritin rises, and CRP shows it | Often |
| Drawn in the afternoonSaturation follows serum iron, which sits highest in the morning and falls over the day by a third or more | Often |
| PregnancyThe transport grows through oestrogen and the baby asks for iron; saturation falls, and usually the store too | Often |
What raises it
Usually iron that just came in, and otherwise iron that cannot get out.
| Cause | How often |
|---|---|
| Iron supplementsAn iron tablet in the hours before the draw fills the taxis temporarily; skip it that day and have blood drawn fasting | Often |
| Iron overloadIn haemochromatosis the gut absorbs too much iron; saturation runs years ahead of ferritin and is the earliest value that gives it away | Sometimes |
| Liver damageA damaged liver releases stored iron; saturation rises and the liver values are abnormal | Sometimes |
How does a transferrin Saturation blood test work?
- Referral
- Not needed. Saturation is calculated from serum iron and transferrin, which are in the iron profile you can have measured yourself.
- Fasting
- Yes, and in the morning, because the value follows serum iron and is highest then. 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 the value down temporarily.
- The draw
- One tube of blood from a vein in your arm. Ferritin and CRP come from the same draw, and without those two saturation cannot be read.
- Repeating
- With a high value first once more fasting and without a supplement; when topping up after a few weeks, because saturation responds earlier than ferritin.
- Which test
- Transferrin Saturation 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 transferrin saturation?
The percentage of your iron transport that is occupied right now: serum iron divided by transferrin. Each transferrin molecule can carry two iron atoms, and saturation says how many of those seats are filled. Where ferritin says how full your store is, saturation says whether it is delivering, and that is the best measure of how much iron your cells can take now.
What is a normal transferrin saturation?
About 20 to 43% where the labs overlap, drawn fasting and in the morning. Below 20% an iron deficiency is likely, above 45% fits iron overload. Later in the day or after an iron tablet those figures do not apply, because the value follows serum iron.
What does a low transferrin saturation mean?
That too little iron is available right now. With a real deficiency the store is empty and ferritin is low too. With an inflammation your body locks the iron away: ferritin is then high, so is CRP, and saturation shows the deficiency that ferritin hides. Drawing in the afternoon or after hard training pushes the value down too, and in pregnancy it falls because the transport grows and the baby asks for iron.
What does a high transferrin saturation mean?
Usually an iron tablet or an iron-rich meal in the hours before the draw; have blood drawn once more fasting and without a supplement. If the value stays above 45%, the transport is full and that is the picture of iron overload, or of a liver releasing stored iron. Ferritin and the liver values say which, and with overload investigation for haemochromatosis belongs, in family members too.
Why is saturation the earliest value for iron overload?
Because in haemochromatosis the gut absorbs too much iron and the transport fills up first, years before the store is so large that ferritin sits high and before there is damage to liver, heart or joints. The condition occurs in about one in two hundred people of Northern European descent, often goes unnoticed for decades through vague symptoms, and is fully treatable by giving blood regularly. A persistent saturation above 45% is therefore the one iron value on which you do not wait.
How does saturation show whether topping up works?
After starting iron, saturation rises within days, long before ferritin moves, because the iron goes straight into the transport. If it stays low, the iron is not being absorbed, and that points at the gut, an inflammation, or a tablet taken with tea, coffee or calcium. Do have blood drawn fasting for that, and not on the day of the tablet itself.
Why does saturation swing over the day?
Because it is calculated from serum iron, and that sits highest in the morning and falls over the day by a third or more. Food with iron and above all an iron tablet lift it within hours, and an inflammation or hard training pushes it down. So always have blood drawn in the morning, fasting and on a rest day, and only compare morning values with each other.
Do I need to fast for a transferrin saturation test?
Yes, and have blood drawn in the morning. Skip an iron tablet the day before and that morning, and choose a rest day. Ferritin and CRP come from the same draw, and without those two saturation cannot be read.
Which tests include transferrin Saturation?
Transferrin Saturation 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): transferrin saturation. 2026. bepalingenklapper.nl
- 2.Certe, test catalogue (Dutch): transferrin saturation. 2026. bepalingenwijzer.certe.nl
- 3.Clinical Diagnostics, lab guide (Dutch): transferrin saturation. 2026. clinicaldiagnostics.nl
- 4.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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