Ferritin vs hemoglobin: what your iron results really say

Low iron is one of the most common gaps worldwide, especially for women. But "iron" on a blood report can mean several different tests, and the one most people get, hemoglobin, is the last to change. Here is how ferritin and hemoglobin fit together.

Two tests, two questions

• Ferritin answers: how much iron is in storage? It is the earliest sign that iron is running low.
• Hemoglobin answers: is there enough iron in your red blood cells to carry oxygen? It only drops once stores are close to empty.

Think of ferritin as your savings account and hemoglobin as your daily spending. You can keep spending normally for months while your savings drain, then run short all at once.

The stages of low iron

1. Low stores: ferritin falls, hemoglobin is still normal. Many people already feel tired at this stage.
2. Iron deficiency: ferritin is very low (often under 15 ng/mL), hemoglobin is at the low end of normal.
3. Iron deficiency anaemia: hemoglobin falls below range, under 13 g/dL for men or 12 g/dL for women.

A normal hemoglobin result on its own does not rule out low iron. That is why ferritin matters.

Reading ferritin

Ferritin is reported in ng/mL (the same number as µg/L). Labs print wide ranges, but a practical reading is:

• Under 15 ng/mL: iron stores are used up.
• 15 to 30 ng/mL: low. Many people feel better above 30.
• Over 300 ng/mL for men, or 200 ng/mL for women: above range. Ferritin also rises with infection, inflammation and liver problems, so a high result is worth a doctor's view.

Why we never suggest iron without a test

Too much iron is harmful, and the body has no good way to get rid of it. That is why our Pro plan, which works from a check-in and no blood test, never recommends iron. When answers point to low iron, it asks you to get a ferritin and hemoglobin test (a CBC) instead.

And when hemoglobin is below range, iron tablets alone are not the answer: low hemoglobin has other causes too, and it needs a doctor to find out which. Our Max plan leaves iron out in that case and says so.

Reference doses

For adults with low ferritin and normal hemoglobin, the reference doses in our rules table are:

• Ferritin under 15 ng/mL: 45 mg elemental iron a day
• Ferritin low but over 15: 30 mg a day

45 mg is the US upper limit for adults. A doctor may suggest more for a short time, but that is their call, not a supplement plan's.

Taking iron well

• Take it in the morning on an empty stomach, or with vitamin C (a glass of orange juice or some amla).
• Keep tea, coffee, milk and calcium 2 hours away. They block iron absorption.
• Every other day can work as well as daily for some people and is easier on the stomach. Ask your doctor if daily iron upsets you.
• Retest ferritin after about 3 months.

Check your iron

Upload your report and Beyond Humans reads ferritin and hemoglobin together, so iron is only suggested when it is likely to help and is safe.