What are the causes of microcytic anemia?

From the Guidelines

Microcytic anemia is primarily caused by iron deficiency, thalassemia syndromes, anemia of chronic disease, sideroblastic anemia, and lead poisoning, with iron deficiency being the most common cause worldwide. These conditions all lead to smaller-than-normal red blood cells (microcytosis) with reduced hemoglobin content, resulting in decreased oxygen-carrying capacity.

Causes of Microcytic Anemia

• Iron deficiency: occurs due to inadequate dietary intake, malabsorption (as in celiac disease), or blood loss (from menstruation, gastrointestinal bleeding, or frequent blood donation) 1
• Thalassemia syndromes: result from genetic defects in hemoglobin synthesis 1
• Anemia of chronic disease: involves impaired iron utilization despite adequate stores, often seen in inflammatory conditions 1
• Sideroblastic anemia: stems from defective heme synthesis 1
• Lead poisoning: interferes with several enzymes in the hemoglobin production pathway 1

Laboratory Findings

• Low MCV (mean corpuscular volume) values below 80 fL 1
• Serum ferritin concentration is the most powerful test for iron deficiency, with a level of <12 μg/dl being diagnostic of iron deficiency 1
• Reticulocyte count can help distinguish between iron deficiency anemia and anemia of chronic disease 1

Treatment

• Depends on addressing the specific underlying cause of the microcytic anemia 1
• Iron supplementation is often used to treat iron deficiency anemia, while anemia of chronic disease may require treatment of the underlying inflammatory condition 1
• Sideroblastic anemia may require treatment with oral iron supplementation and/or erythrocyte transfusions, with monitoring of iron status to detect toxic iron loading 1

From the Research

Microcytic Anaemia Causes

• Iron deficiency anemia is the most common cause of microcytic anemia, as stated in studies 2, 3, 4, 5, 6
• Other causes of microcytic anemia include:
  • Thalassemia, a genetic disorder that affects the production of hemoglobin 3, 4, 5
  • Sideroblastic anemia, a disorder that affects the production of hemoglobin 3, 4
  • Anemia of chronic disease, a condition that occurs in people with chronic diseases such as kidney disease or cancer 2, 4
  • Alpha-thalassemia, a genetic disorder that affects the production of hemoglobin 5
• Microcytic anemia can also be caused by:
  • Bleeding, such as menstrual or gastrointestinal bleeding 2, 6
  • Impaired iron absorption, such as in celiac disease or after bariatric surgery 6
  • Inadequate dietary iron intake 6
  • Pregnancy, which can lead to iron deficiency anemia due to increased iron requirements 6

Diagnosis and Evaluation

• The diagnosis of microcytic anemia is typically made by measuring the mean corpuscular volume (MCV) of red blood cells, which is less than 80 mcm3 in adults 3
• Other laboratory tests that may be used to evaluate microcytic anemia include:
  • Serum ferritin, which measures iron stores 2, 4, 6
  • Serum iron, which measures the amount of iron in the blood 4
  • Total iron binding capacity, which measures the amount of iron that can be bound by transferrin 4
  • Hemoglobin electrophoresis, which measures the different types of hemoglobin in the blood 4

Treatment and Management

• The treatment of microcytic anemia depends on the underlying cause, but may include:
  • Iron supplements, such as oral iron or intravenous iron 2, 3, 6
  • Treatment of underlying conditions, such as celiac disease or chronic kidney disease 6
  • Avoidance of bleeding, such as by treating menstrual or gastrointestinal bleeding 6