Iron and Ferritin: Finding Low Iron, and Fixing It
Labs and nutrition · Energy
You can run low on iron long before your blood count shows it. Here is how we find it and fix it, and why taking it every other day may work better.
Written for my patients. If you are not one, read "call me" as "call your own clinician", and take the questions here to them.
What iron does
Iron carries oxygen in your red blood cells and helps muscles, brain, and thyroid work. Your body stores extra iron, and ferritin is the lab that measures those stores. Iron stores usually run out first. Anemia, a low red blood cell count, comes later.
Signs you may be low
Fatigue, feeling short of breath on stairs, restless legs, hair shedding, headaches, brittle nails, feeling cold, and craving ice. Many people with low iron stores feel tired without being anemic.
The labs
| Test | What it tells us |
|---|---|
| Ferritin | Your iron stores. Under 30 means low iron stores. If you are anemic, gut specialists use under 45 as the cutoff. |
| CBC | Hemoglobin and red cell size show whether low iron has caused anemia yet. |
| Iron and saturation | Useful alongside ferritin, especially when inflammation makes ferritin look falsely normal. |
Why people run low
Taking iron the right way
- Every other day often works as well or better than daily. A single dose raises a hormone (hepcidin) that blocks absorption of the next day's dose. Alternate-day dosing also causes less stomach upset.
- Take it on an empty stomach if you can, or with a little food if it bothers you.
- Keep coffee, tea, calcium, dairy, and antacids at least 2 hours away. They block absorption.
- Keep it at least 4 hours from thyroid medicine.
- Dark stools are normal on iron. Constipation is common.
- We recheck ferritin and your blood count in about 8 to 12 weeks. Refilling stores takes months.
If pills do not work
Some people cannot absorb or tolerate iron pills. IV iron refills stores in one or two visits and is safe and effective. It is the right choice after weight-loss surgery, with celiac disease or inflammatory bowel disease, or when pills have not worked.
Do not take iron without testing
I wrote this for my patients, and it reads the same for everyone: general information, not a plan. If you would like your own numbers read against your own story, that is what a Lab Second Look is for. If you are not sure where to start, the free intro call is fifteen minutes.
A note on how to use this. General information for my patients, not individualized advice. Keep iron pills away from children; an overdose is dangerous for them.
- Ko CW et al. AGA clinical practice guidelines on the gastrointestinal evaluation of iron deficiency anemia. Gastroenterology 2020;159(3):1085–94.
- Stoffel NU et al. Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split dosing in iron-depleted women. Lancet Haematol 2017;4(11):e524–33.
- Stoffel NU et al. Iron absorption from supplements is greater with alternate day than with consecutive day dosing in iron-deficient anemic women. Haematologica 2020;105(5):1232–9.
Trang Ca Laube, FNP-BC, FMACP · Reclaim Power Telehealth · Updated September 2026
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