Iron deficiency is the most common micronutrient deficiency in the world. Iron is needed not only for hemoglobin: it takes part in energy production in the mitochondria, in thyroid function and in neurotransmitter synthesis.
The key point: the deficiency develops in three stages, and anemia is only the last of them. Long before hemoglobin falls, iron stores are already depleted and symptoms are already present.
Reference ranges
The three stages of deficiency — and what the tests show at each:
| 1. Store depletion (latent) | ferritin low, hemoglobin normal |
| 2. Iron-deficient erythropoiesis | ferritin low, transferrin saturation falls |
| 3. Iron-deficiency anemia | both ferritin and hemoglobin reduced |
| Deficiency threshold by ferritin | below 30 ng/mL |
What an elevated level means
The opposite situation is iron overload. It occurs with hereditary hemochromatosis, frequent blood transfusions or uncontrolled iron supplementation.
Excess iron is toxic: it is deposited in the liver, pancreas and heart, causing cirrhosis, diabetes and cardiomyopathy. That is why you must not take iron "preventively" without tests.
What a low level means
Here "low" is the essence of the condition. Symptoms of deficiency: chronic fatigue and weakness, hair loss, brittle nails, dry skin, pallor, shortness of breath and palpitations on exertion, feeling cold, restless legs syndrome, reduced concentration and memory, taste distortion (a craving to eat ice or chalk).
Causes in women are most often heavy periods and pregnancies. In men and postmenopausal women, iron deficiency requires a mandatory search for a source of blood loss in the GI tract: it can be the first sign of a serious disease.
How the test is done
Minimum set: ferritin (stores) + a complete blood count (hemoglobin, MCV) + C-reactive protein (to see whether ferritin is falsely raised by inflammation).
For a fuller picture, add serum iron, transferrin and transferrin saturation. Stop iron supplements at least a week before testing, otherwise the result will be inflated.
What affects the value
- Blood loss — heavy periods, hidden GI bleeding, blood donation.
- Absorption — celiac disease, atrophic gastritis, proton-pump inhibitors.
- Diet — vegetarianism: non-heme iron is absorbed far worse than heme iron.
- Vitamin C — improves absorption; tea, coffee and calcium — worsen it.
- Pregnancy and lactation — sharply raise the requirement.
- Intense training — endurance athletes have higher iron losses.
Calculate using this marker
Calculators where Iron deficiency is used directly:
Frequently asked questions
How do I know I have iron deficiency if my hemoglobin is normal?
By ferritin. It falls first — long before hemoglobin. A value below 30 ng/mL indicates depleted stores even with a perfect complete blood count. This is latent deficiency, and it already causes fatigue and hair loss.
Can I replenish iron with food alone?
With latent deficiency — sometimes yes; with anemia — usually no. Too little iron is absorbed from food to refill depleted stores within a reasonable time. Supplements are usually needed, and a doctor should prescribe them: their dose and duration are set by tests.
Why not take iron "just in case"?
Because excess iron is toxic: it is deposited in the liver, heart and pancreas. Iron intake also distorts the tests. First ferritin — then a decision.