Transferrin Saturation Calculator
Serum iron divided by TIBC, with unbound iron-binding capacity and a low, normal, or high read.
What it does
Transferrin saturation measures how much of the blood's iron-carrying capacity is actually filled. Serum iron is the amount of iron circulating at the moment of the draw. Total iron-binding capacity, or TIBC, estimates how much iron the transport protein transferrin could hold. Divide the first by the second and the result is the percentage of transferrin binding sites that are occupied.
The test belongs to a group called iron studies, usually ordered with ferritin. Saturation below about 20 percent suggests the body is short on iron, because transferrin is waiting for cargo that is not arriving. Saturation above about 50 percent suggests the opposite problem, iron overload or increased iron turnover, and is one of the signals used when screening for hereditary hemochromatosis.
The default example is a serum iron of 60 µg/dL and a TIBC of 350 µg/dL. The saturation is 60 / 350 = 0.1714, or 17.1 percent, which falls below the usual band and reads as low. The unbound iron-binding capacity is 350 - 60 = 290 µg/dL, the room left on transferrin.
The numbers are easy to misread because serum iron moves during the day and rises after an iron supplement or an iron-rich meal. TIBC also shifts with inflammation, liver disease, and nutrition. A single low saturation is a clue, not a diagnosis, and it is normally interpreted with ferritin, the blood count, and the clinical setting.
Reference bands vary by laboratory and by population. The 20 to 50 percent band used here is a common adult convention, and some laboratories use 15 to 50 percent or a sex-specific range. Always compare the result with the interval printed on the report that produced the numbers.
How to use
- Find serum iron on the iron studies panel, usually in µg/dL.
- Find TIBC on the same panel, also in µg/dL.
- Enter both values without converting units.
- Read the saturation percentage first.
- Read the unbound iron-binding capacity as the remaining capacity.
- Compare the status band with the reference range on the laboratory report.
Formula
- Serum iron
- Iron circulating in the blood at the time of the draw, in µg/dL.
- TIBC
- Total iron-binding capacity, the maximum iron transferrin could carry, in µg/dL.
- Saturation
- Share of transferrin binding sites occupied by iron, in percent.
- UIBC
- Unbound iron-binding capacity, the unused portion of TIBC, in µg/dL.
Both inputs must be in the same units, which is normally µg/dL in the United States and µmol/L in some other countries. The status bands shown are adult conventions; pregnancy, age, and laboratory method can shift them. Saturation should be interpreted with ferritin and the blood count rather than on its own.
Worked example
Example: serum iron 60 µg/dL with TIBC 350 µg/dL
An iron studies panel reports a serum iron of 60 µg/dL and a TIBC of 350 µg/dL.
- Divide serum iron by TIBC: 60 / 350 = 0.1714.
- Multiply by 100: 0.1714 x 100 = 17.1 percent.
- Subtract to find UIBC: 350 - 60 = 290 µg/dL.
- Compare the saturation with the adult band of 20 to 50 percent.
- 17.1 percent is below 20, so the status reads as low.
- Read the result alongside ferritin and the blood count before drawing conclusions.
Reference table
| Serum iron | Saturation | UIBC | Status |
|---|---|---|---|
| 40 µg/dL | 11.4 % | 310 µg/dL | Low |
| 70 µg/dL | 20.0 % | 280 µg/dL | Normal |
| 140 µg/dL | 40.0 % | 210 µg/dL | Normal |
| 210 µg/dL | 60.0 % | 140 µg/dL | High |
Limits
- Uses a common adult band of 20 to 50 percent; laboratory and population ranges vary.
- Serum iron fluctuates during the day and after supplements or meals.
- TIBC changes with inflammation, liver disease, and nutritional status.
- Does not diagnose iron deficiency or overload on its own; ferritin and clinical context are required.
Common mistakes
- Mixing µg/dL and µmol/L without converting.
- Taking an iron supplement shortly before the blood draw.
- Reading saturation without ferritin, which can be low while saturation is normal in inflammation.
- Using a single result to diagnose hemochromatosis instead of the recommended screening sequence.
- Assuming the same reference band applies in pregnancy or in children.
Try it yourself
Quick checks. Answers sit tucked under each question.
Serum iron 100 µg/dL, TIBC 300 µg/dL. What is the saturation?
33.3 percent, with a UIBC of 200 µg/dL and a normal status.
Serum iron 180 µg/dL, TIBC 300 µg/dL. What is the saturation?
60.0 percent, with a UIBC of 120 µg/dL and a high status.
Serum iron 40 µg/dL, TIBC 350 µg/dL. What is the saturation?
11.4 percent, with a UIBC of 310 µg/dL and a low status.
Questions
What does transferrin saturation mean?
It is the percentage of transferrin iron-binding sites that are occupied by iron at the time of the blood draw.
What is a normal transferrin saturation?
Many laboratories use roughly 20 to 50 percent for adults, though the exact range varies by laboratory and population.
Why is my saturation low but my ferritin normal?
Inflammation can raise ferritin while lowering saturation. The two tests answer different questions and are read together.
Can I eat before the test?
Follow the laboratory's instructions. Many panels are drawn fasting because recent iron intake can raise serum iron.
Is high saturation always iron overload?
No. It can occur with increased iron turnover, liver disease, or recent supplements. High saturation is a signal for further testing, not a diagnosis.
What is UIBC?
Unbound iron-binding capacity, the part of TIBC not occupied by iron, calculated as TIBC minus serum iron.
Sources
- CDC NHANES: Serum iron and TIBC laboratory method
- MedlinePlus: TIBC and iron blood test
- AAFP: Iron deficiency anemia in adults