Short answer: Iron tests are a small group of blood tests: ferritin, which reflects how much iron the body has in storage; serum iron, the iron circulating in the blood; and transferrin saturation (and sometimes TIBC), which shows how much of the iron-carrying protein is loaded. Doctors read them together, often with a complete blood count.
At a glance
| Ferritin | Iron in storage |
|---|---|
| Serum iron | Iron circulating in the blood; varies through the day |
| Transferrin saturation | How loaded the iron-carrying protein is |
| Units | ng/mL or µg/L (ferritin); µg/dL or µmol/L (iron); % (saturation) |
| LOINC | 2276-4 (ferritin), 2498-4 (iron), 2502-3 (saturation) |
| Read with | The complete blood count; ferritin also rises with inflammation |
What the test measures
Iron is needed to make haemoglobin. Most of it is in red cells, and the rest is stored, mainly as ferritin in the liver and other tissues. A small amount of ferritin circulates in the blood and follows the size of the stores.
Serum iron changes during the day and after a meal, so on its own it says little. Transferrin is the protein that carries iron; transferrin saturation is the percentage of it that carries iron at the moment of the test.
When it is ordered
Common reasons, which your doctor adapts to you:
- when a blood count shows anaemia or small red cells;
- when tiredness, hair loss or heavy periods need checking;
- to follow iron treatment, or to check for iron overload.
How the result is written on the report
| Result on the report | LOINC code | Usual unit | Also seen as |
|---|---|---|---|
| Ferritin | 2276-4 | ng/mL | µg/L (same number) |
| Serum iron | 2498-4 | µg/dL | µmol/L (×0.179) |
| Transferrin saturation | 2502-3 | % | — |
| Haemoglobin (often on the same report) | 718-7 | g/dL | g/L |
Ferritin in ng/mL and µg/L is the same number. Serum iron in µg/dL converts with µmol/L = µg/dL × 0.179 (100 µg/dL ≈ 17.9 µmol/L).
Reading your report
Ferritin is also an 'acute-phase' protein: it rises with infection, inflammation and some liver conditions, so a normal ferritin does not always rule out low iron stores. That is why doctors may look at CRP at the same time. Serum iron is best taken in the morning and fasting, as your lab advises. Do not start or stop iron supplements based on one result without asking your doctor.
Keeping the results in your record
Scan or photograph the report in Anpheros Daily: each value is read with its unit and the laboratory's reference range, you check it, and it is stored with its LOINC code as an HL7 FHIR Observation, a format used by many hospitals and national health systems. Results from different laboratories line up on one chart over time, and the lab unit converter helps when two reports use different units. Our guide on how to read lab results explains reference ranges and flags in general; the lab results guide for a new doctor shows how to share them.
What this page does not do
It explains what the test is and how the result is written. It does not interpret your result, diagnose or recommend treatment: the meaning of a value depends on your history, your other results and how the sample was taken, and that is your doctor's job.
Related pages
Sources
Frequently asked questions
What is the difference between ferritin and serum iron?
Ferritin reflects the iron stored in the body; serum iron is the iron circulating at that moment. They can point in different directions.
Can ferritin be high because of inflammation?
Yes. Infection and inflammation can raise ferritin even when iron stores are not high, which is why it is read with other results.
Is ng/mL the same as µg/L for ferritin?
Yes, the number is the same in both units.
Should I fast before an iron test?
For serum iron, labs often ask for a morning, fasting sample. Ferritin is less affected. Follow your lab's instructions.
Try it in Anpheros Daily
Photograph your lab report and Anpheros Daily lines up each value with its reference range, so you can compare reports from different laboratories.
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