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The guide

Transferrin saturation: how full the taxis are.

Updated 2 min readWaiting for medical review

The short answer

Transferrin is the protein that carries iron in your blood, and saturation is the share of it carrying iron right now. Under about 30% on a day you took no iron points to a shortage. The Iron Guide aims for 30 to 45%.

Picture transferrin as a fleet of taxis and iron as the passengers. On a normal day about a third of the seats are taken. When iron runs short, your liver sends out more taxis to look for it, so transferrin goes up while the share of full seats goes down.

1 The gut: the doorAbout 10% of the ironyou eat gets in.HEPCIDIN, THE DOORMAN2 Transferrin: the taxiCarries iron in your blood.About a third of seats are taken.3 Ferritin: the storageThousands of flats, eachholding iron until needed.4 Bone marrowBuilds new red cells,each one full of iron.5 Red cells live 3–4 months6 RecyclingSpleen and liver sendold cells’ iron back.The one big exit: blood lossEvery period takes iron with it.
The iron cycle. Transferrin carries iron from your gut and your recycled red cells to the marrow and the stores.
  • %30–45The guide's goal, on a day without iron
  • %45–60Can be fine while you take iron
  • %60Above this, ask your doctor

How to read it

ResultOften means
Under 20%Iron is short in your blood. Read it next to ferritin.
20–30%Borderline, and common when stores are low.
30–45%Within the guide's goal.
45–60% during a course of ironUsually expected while you take iron.
Over 60%Possibly too much iron for now. Ask your doctor.

Test it properly

Saturation is calculated from serum iron, which jumps after a meal or a tablet. So it only means something from a morning, fasting test, ideally after a few days without iron supplements. Test iron, ferritin, transferrin and saturation from the same blood draw. See how to prepare.

Low protein can keep transferrin low even when iron is short, which makes saturation look better than it is. Total protein and albumin belong on the same panel.

Questions

Is a high transferrin good or bad?

Transferrin goes up when iron is short, because your liver makes more carriers. A high transferrin with a low saturation fits low iron.

Why is my saturation high but my ferritin low?

Most often because you took iron or ate an iron-rich meal shortly before the test, which pushes serum iron up for hours. Repeat it fasting, after a few days without supplements.

Sources

  1. 1.NIH Office of Dietary Supplements. Iron: fact sheet for health professionals
  2. 2.World Health Organization. Guideline on use of ferritin concentrations to assess iron status in individuals and populations, 2020
  3. 3.The Iron Guide, part 3: Your numbers

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.

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