Ferritin: The Iron Marker That Deserves More Attention

Written By Sadie Carlsen

by Sadie Carlsen NP

Founder, FunctNP Functional Medicine
Meridian, Idaho

Ferritin is one of the most useful—and often overlooked—markers when evaluating fatigue, hair loss, exercise intolerance, brain fog, and even certain blood sugar patterns.

Ferritin reflects your body’s stored iron. While a standard CBC can tell us whether someone is anemic, ferritin can become low before anemia develops. That means a person can have a “normal” hemoglobin and still have depleted iron stores.

Low ferritin may be associated with symptoms such as fatigue, weakness, shortness of breath with exertion, headaches, restless legs, hair shedding, poor exercise recovery, difficulty concentrating, and feeling cold.

For women, low ferritin is especially common because of menstrual blood loss, pregnancy, postpartum changes, dietary intake, gastrointestinal issues, and difficulty absorbing iron.

Another reason ferritin matters is that iron status can sometimes influence how we interpret other laboratory markers.

One example is A1C.

A1C estimates average blood glucose by measuring glucose attached to hemoglobin inside red blood cells. Because the test depends partly on red blood cell lifespan and turnover, iron deficiency can sometimes make A1C appear higher than the overall glucose picture would suggest.

That does not mean every elevated A1C is caused by low ferritin. It means context matters.

When A1C seems inconsistent with fasting glucose, continuous glucose monitor data, or symptoms, it may be helpful to look at the bigger picture, including:

  • Ferritin

  • CBC

  • Serum iron and iron saturation

  • TIBC or transferrin

  • Fasting glucose

  • Fasting insulin

  • Fructosamine

  • Continuous glucose monitoring when appropriate

Functional medicine is not about chasing one isolated laboratory number. It is about asking whether the numbers make sense together.

If your ferritin is low, your A1C is borderline, or you have symptoms that have not been fully explained, a more comprehensive evaluation may help uncover what is actually going on.

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Sadie Carlsen
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