The short answer
Serum iron is the iron moving through your blood at the moment of the test, and it jumps after every meal or tablet. Ferritin is your stored iron and moves over months. To track your progress, follow ferritin.
Think of serum iron as today's traffic and ferritin as your savings. A single test can catch serum iron at rush hour, just after breakfast or a supplement, or in a quiet moment. That is why it says little on its own, and why labs report it with transferrin and saturation.
| Serum iron | Ferritin | |
|---|---|---|
| What it is | Iron in transit | Iron in storage |
| Moves | Within hours | Over weeks and months |
| Pushed up by | A meal or tablet before the test | Inflammation, as well as real stores |
| The guide's goal | 15–30 µmol/L | 50–80 µg/L |
| Use it for | Working out saturation | Tracking your stores |
When they disagree
- High iron, low ferritin: often a supplement or a meal before the test. Repeat it fasting.
- Normal iron, low ferritin: stores are running down while transport still copes.
- Low iron, high ferritin: think of inflammation and check CRP. See inflammation and ferritin.
Test ferritin, iron, transferrin and saturation together, in the morning, fasting.
Take your iron supplement the evening before a test.
US labs report serum iron in µg/dL. Multiply µmol/L by 5.6 to convert, or use the unit converter.
Questions
Which matters more, iron or ferritin?
For your stores, ferritin. Serum iron matters mostly as the input to transferrin saturation.
Can ferritin be normal while serum iron is low?
Yes, for example after an illness, when inflammation pushes ferritin up and pulls serum iron down at the same time.
Sources
- 1.NIH Office of Dietary Supplements. Iron: fact sheet for health professionals
- 2.Ganz T. Hepcidin and iron regulation, 10 years later. Blood, 2011
- 3.The Iron Guide, part 2: How iron moves
This page has not been reviewed by a clinician yet. Read it as general education, and take your own results to your doctor.
Educational, not medical advice. ferritin.ai does not diagnose or treat any condition, and it never sets a dose. Talk to your doctor about your own results.