Overview.
Iron deficiency anemia is the most common type of anemia worldwide, affecting an estimated 2 billion people. It occurs when your body lacks sufficient iron to produce hemoglobin, the protein in red blood cells that carries oxygen. The good news: it's highly treatable once diagnosed. The challenge: symptoms are often dismissed as 'just fatigue,' delaying diagnosis for years.
Iron is essential for producing hemoglobin, which gives red blood cells their oxygen-carrying capacity. When iron stores are depleted, your body can't make enough functional hemoglobin. Red blood cells become smaller (microcytic) and paler (hypochromic). Iron deficiency progresses through stages: depleted stores (low ferritin) → iron-deficient erythropoiesis → frank anemia (low hemoglobin).
Prevalence: Iron deficiency is the most common nutritional deficiency worldwide. In the U.S., it affects about 10% of women of reproductive age, 5% of adolescents, and 2% of adult men. Globally, iron deficiency anemia affects about 30% of the world's population, particularly in developing countries.
Medical name: Iron Deficiency Anemia (IDA)
Symptoms.
Early warnings
- Fatigue not relieved by rest
- Decreased exercise tolerance
- Shortness of breath during activity
- Difficulty concentrating
- Pale skin or pale inner eyelids
- Cold hands and feet
- Cravings for ice or non-food items (pica)
- Brittle nails or hair loss
Classic symptoms
- Pronounced fatigue and weakness
- Pallor (pale skin, nail beds, mucous membranes)
- Shortness of breath, especially with exertion
- Dizziness or lightheadedness
- Headaches
- Cold extremities
- Pica (craving ice, dirt, starch)
- Restless legs syndrome
- Glossitis (inflamed tongue)
- Angular cheilitis (cracked corners of mouth)
- Brittle nails (koilonychia—spoon-shaped in severe cases)
Progression
Iron deficiency progresses through three stages: (1) Storage depletion—ferritin drops but hemoglobin is normal; (2) Iron-deficient erythropoiesis—serum iron and saturation drop, RBCs become smaller; (3) Frank anemia—hemoglobin falls below normal. Symptoms typically appear in stage 2 or 3.
Risk factors.
- Menstruating women (especially heavy periods)
- Pregnancy and breastfeeding
- Vegetarian or vegan diet
- GI conditions affecting absorption (celiac, IBD, gastric surgery)
- Regular blood donation
- Endurance athletes (foot-strike hemolysis, GI bleeding, sweating)
- Chronic blood loss (ulcers, hemorrhoids, NSAIDs)
- Infants and toddlers during rapid growth
- Adolescents during growth spurts
Lab interpretation.
Key biomarkers
- Ferritin — <30 ng/mL is depleted stores; <15 ng/mL is diagnostic for iron deficiency (primary)
- Hemoglobin — <12 g/dL (women) or <13 g/dL (men) indicates anemia (primary)
- MCV — <80 fL (microcytic) is classic for iron deficiency (primary)
- Serum Iron — Low (<60 µg/dL) (secondary)
- TIBC — Elevated (>400 µg/dL) as body tries to capture more iron (secondary)
- Iron Saturation — Low (<20%) indicates insufficient iron delivery (secondary)
- RDW — Often elevated (>14.5%) showing cell size variation (supportive)
Diagnostic criteria
- Ferritin <30 ng/mL (or <50 in context of inflammation) indicates depleted stores
- Hemoglobin <12 g/dL (women) or <13 g/dL (men) confirms anemia
- Low iron saturation (<20%) with elevated TIBC supports diagnosis
- Microcytosis (MCV <80 fL) is typical but may be absent early
- Response to iron therapy confirms diagnosis retrospectively
Recommended panels
When & next steps.
When to test
- Fatigue not explained by other causes
- Heavy menstrual bleeding
- Vegetarian or vegan diet
- GI symptoms or known GI conditions
- During pregnancy (routine screening)
- Athletes with declining performance
- Pica (craving ice or non-food items)
- Unexplained pallor
- Before and after blood donation
If suspected
- Order CBC with iron studies (ferritin, iron, TIBC, saturation)
- Check reticulocyte count to assess bone marrow response
- Consider vitamin B12 and folate to rule out combined deficiency
- Review menstrual history in women
- Ask about GI symptoms, NSAID use, blood donation
If confirmed
- Identify the cause (blood loss, poor intake, malabsorption)
- GI evaluation if no clear source (endoscopy/colonoscopy in older adults)
- Iron supplementation: typically 30-60 mg elemental iron daily
- Take with vitamin C on empty stomach for better absorption
- Expect hemoglobin to improve in 2-4 weeks
- Continue 3-6 months to replenish ferritin stores
- Recheck ferritin after repletion to confirm recovery
FAQs.
Why is ferritin the most important test?
Ferritin reflects your iron stores—the total iron your body has banked. It drops before hemoglobin does, making it the earliest and most sensitive marker. You can be iron-deficient with normal hemoglobin if ferritin is low.
How long does it take to correct iron deficiency?
Hemoglobin typically improves within 2-4 weeks of starting iron. However, replenishing ferritin stores takes 3-6 months of continued supplementation. Don't stop when you 'feel better'—complete the course.
Why do I feel worse when I take iron supplements?
Iron supplements commonly cause GI side effects (nausea, constipation). Taking with food reduces absorption but improves tolerance. Consider lower-dose or alternate-day dosing, which may be equally effective with fewer side effects.
Can I get enough iron from diet alone?
Mild deficiency may respond to dietary iron (red meat, legumes, fortified cereals with vitamin C). Significant deficiency usually requires supplements. Heme iron (meat) is absorbed much better than non-heme iron (plants).