(IDA) is the most common form of anemia worldwide and can be due to inadequate intake, decreased absorption (e.g., atrophic gastritis, inflammatory bowel disease), increased demand (e.g., during pregnancy), or increased loss (e.g., gastrointestinal bleeding, menorrhagia) of iron. Prolonged deficiency depletes the iron stores in the body, resulting in decreased erythropoiesis and anemia. Symptoms are nonspecific and include fatigue, pallor, lethargy, hair loss, brittle nails, and pica. Diagnostic lab values include low hemoglobin, microcytic, hypochromic red blood cells on peripheral smear, and low ferritin and iron levels. Once diagnosed, the underlying cause should be determined. Patients at risk for underlying gastrointestinal malignancy should also undergo a colonoscopy. Iron deficiency anemia is treated with oral (most common) or parenteral iron supplementation. Severe anemia or those with concomitant cardiac conditions may also require blood transfusions. The underlying cause of IDA should also be corrected.
- Most common form of anemia worldwide 
- ∼ 3% of the general population in the United States is affected 
- Ethnic variations: African-American and Mexican-American populations in the US are at increased risk.
Prevalence highest in: 
- Children up to 5 years of age
- Young women of child-bearing age (due to menstrual blood loss)
- Pregnant women
Epidemiological data refers to the US, unless otherwise specified.
The most common causes of IDA can be divided by age groups and pathophysiologic mechanisms.
Based on age 
- Malnutrition (mainly resource-limited countries)
- Excessive intake of cow's milk (> 24 ounces/700 mL per day)
- Adolescence: menarche/menstruation
- Adults (20–50 years)
- Adults > 50 years
Based on underlying mechanism 
- Meckel diverticulum
- Dialysis-dependent renal failure
- Frequent blood donation
Decreased iron intake
- Chronic undernutrition
- Cereal-based diet
- Strict vegan diet 
- Decreased iron absorption
- Increased demand
- Signs and symptoms of anemia
- Brittle nails, koilonychia (spoon-like nail deformity); , hair loss
- Pica, dysphagia
- Angular cheilitis: inflammation and fissuring of the corners of the mouth 
- Atrophic glossitis: erythematous, edematous, painful tongue with loss of tongue papillae (smooth, bald appearance)
- IDA can be associated with Plummer-Vinson syndrome (PVS) 
- Diagnosis of IDA requires the presence of anemia (low hemoglobin or hematocrit) and evidence of low iron stores (usually determined by serum ferritin and iron levels).
- IDA typically manifests as microcytic, hypochromic anemia with anisocytosis, low serum ferritin, and low serum iron levels.
Laboratory tests 
Complete blood count with differential
- ↓ Hemoglobin: anemia is typically defined as a hemoglobin level less than 2 SD below normal (for age and sex) 
- ↓ Hematocrit
- RBC: initially normal (decreased with prolonged deficiency)
- ↓ Mean corpuscular volume: microcytic
- ↓ Mean corpuscular hemoglobin: hypochromic
- Normal or ↓ reticulocyte count
- ↑ (RDW) : differentiates IDA from anemia of chronic disease and thalassemia trait (where the RDW is usually normal)
- ↑ Platelet count (reactive thrombocytosis) 
- Iron studies
- Peripheral blood smear: anisocytosis and hypochromasia (increased zone of central pallor)
- Bone marrow biopsy: (rarely indicated): In patients with suspected IDA and nondiagnostic iron studies, low bone marrow iron is diagnostic of IDA.
Evaluation for underlying cause 
Occult gastrointestinal bleeding
- Recommended for:
- Initial workup
- If no risk factors (e.g., advanced age) for occult GI bleeding, consider treating empirically with oral iron and monitor for response
- Evaluation for menorrhagia, , , , etc.
- See “ .”
- Examination of stool for ova and parasites if concern for Ancylostoma duodenale, Necator americanus (e.g., patient from a resource-limited country, eosinophilia on CBC ) 
- Repeat stool tests may be necessary since egg-laying may be delayed.
- Note that hookworms can also cause a positive stool occult blood test.
- Dietary modifications
Oral iron therapy
- Indicated in all patients with IDA (if tolerated)
- Should initially be administered for 3–6 months 
- Adverse effects: gastrointestinal discomfort, nausea, constipation, black discoloration of stool
- Absorption may be enhanced by simultaneous consumption of vitamin C (e.g., with lime juice).
- Foods (e.g., tea, cereals) and drugs (e.g., calcium, antacids, PPIs) that decrease intestinal absorption of iron should be avoided.
Parenteral iron therapy
- Indicated in
- Available forms (ferric preparations): iron dextran, iron sucrose, and sodium ferric gluconate
- Adverse effects
- Blood transfusion
- Treat the underlying disease (e.g., antihelminthics for hookworm, OCPs for menorrhagia)
See "Diagnostics" in “.”
- Acute blood loss anemia
- Occult bleeding
- : Serum ferritin levels and transferrin saturation levels are normal or increased.
- (esp. in children)
- co-exist with IDA) (may : Serum ferritin levels and transferrin saturation levels are usually normal.
|Iron deficiency anemia||Anemia of chronic disease|
|Ferritin||↓||Normal to ↑|
|Iron||↓||normal to ↓|
|Transferrin saturation||↓||Normal to slightly ↓|
|Soluble transferrin receptor (sTfR)||↑||normal|
The differential diagnoses listed here are not exhaustive.
Special patient groups
- Etiology: increased iron requirements
- Treatment: oral or IV iron supplementation (see “Treatment” above) 
- Increased risk of adverse pregnancy outcomes
- Impaired fetal neurodevelopment