Microcytic Anemia: Causes, Symptoms and Treatment

What Is Microcytic Anemia?

Microcytic anemia is a form of anemia characterized by red blood cells (erythrocytes) that are smaller than normal. The term comes from the Greek words mikros (small) and kytos (cell). Because the red blood cells are undersized, they carry less hemoglobin and are less efficient at transporting oxygen throughout the body. In laboratory terms, microcytic anemia is defined by a mean corpuscular volume (MCV) below 80 femtoliters (fL).

Causes

The most common cause of microcytic anemia is iron deficiency. Iron is essential for the synthesis of hemoglobin, the oxygen-carrying protein in red blood cells. When iron is lacking, hemoglobin production decreases and red blood cells remain abnormally small. Other significant causes include:

• Iron deficiency anemia: The most prevalent cause worldwide; results from inadequate dietary intake, poor absorption, or chronic blood loss (e.g., heavy menstruation, peptic ulcers, or colorectal polyps).
• Thalassemia: An inherited disorder affecting hemoglobin production.
• Anemia of chronic disease: Chronic inflammation, infections, or malignancies can impair iron utilization in the body.
• Sideroblastic anemia: A condition in which iron cannot be properly incorporated into hemoglobin despite sufficient availability.
• Lead poisoning: Lead inhibits hemoglobin synthesis and may lead to microcytic anemia.

Symptoms

Symptoms of microcytic anemia arise from reduced oxygen delivery to tissues. Common symptoms include:

• Persistent fatigue and weakness
• Pallor of the skin, mucous membranes, and nail beds
• Shortness of breath and dizziness, especially during physical activity
• Headaches and difficulty concentrating
• Rapid or irregular heartbeat (tachycardia)
• In iron deficiency specifically: brittle nails, hair loss, and cracked corners of the mouth (angular cheilitis)

Diagnosis

Microcytic anemia is primarily diagnosed through a blood test. Key laboratory parameters include:

• Complete blood count (CBC): Reveals low hemoglobin levels and an MCV below 80 fL.
• Serum ferritin and serum iron: Used to assess iron stores and availability.
• Transferrin saturation: Indicates how much iron is bound to the transport protein transferrin.
• Reticulocyte count: Evaluates bone marrow activity and red blood cell production.
• Hemoglobin electrophoresis: Used to rule out thalassemia and other hemoglobinopathies.

In some cases, imaging studies or endoscopy may be necessary to identify a source of chronic blood loss.

Treatment

Treatment depends on the underlying cause of the microcytic anemia:

Iron Deficiency Anemia

The primary treatment is iron supplementation, administered orally as tablets or intravenously as an infusion in cases of severe deficiency or poor oral tolerance. The underlying cause of iron loss (e.g., a bleeding source) must also be identified and treated. A diet rich in iron — including red meat, legumes, and dark leafy vegetables — supports recovery.

Thalassemia

Mild forms often require no treatment. Severe thalassemia may necessitate regular blood transfusions and potentially a stem cell transplant.

Anemia of Chronic Disease

Treatment focuses on managing the underlying condition. Supplemental iron or erythropoietin (a hormone stimulating red blood cell production) may be used as adjunct therapy.

When to See a Doctor

Persistent fatigue, unexplained pallor, or shortness of breath should prompt a medical evaluation. Pregnant women, children, and individuals with chronic illnesses are at higher risk for anemia and should undergo regular blood monitoring.

References

1. World Health Organization (WHO): Nutritional Anaemias: Tools for Effective Prevention and Control. Geneva: WHO Press, 2017.
2. Kasper DL et al.: Harrison's Principles of Internal Medicine, 21st Edition. McGraw-Hill Education, 2022.
3. Camaschella C.: Iron-Deficiency Anemia. New England Journal of Medicine, 2015; 372(19): 1832–1843.