What are the causes of microcytic anemia (small red blood cell anemia)?

From the Guidelines

Microcytic anemia, excluding common causes like iron deficiency, thalassemias, and hemoglobinopathies, can be caused by genetic disorders of iron metabolism or heme synthesis, such as sideroblastic anemia, which involves defective heme synthesis and can be inherited or acquired. These disorders can lead to a range of clinical presentations, including microcytic anemia, and can be diagnosed through a combination of laboratory tests, including complete blood count, serum iron, ferritin, and total iron binding capacity, as well as genetic analysis 1.

Key Causes

• Sideroblastic anemia, which can be inherited or acquired, and involves defective heme synthesis
• Genetic disorders of iron metabolism, such as those affecting the SLC11A2 gene
• Other rare genetic disorders affecting heme synthesis or iron metabolism

Diagnostic Approach

• Measure complete blood count, serum iron, ferritin, and total iron binding capacity to assess iron status and rule out common causes of microcytic anemia
• Use genetic analysis to diagnose genetic disorders of iron metabolism or heme synthesis, such as sideroblastic anemia due to defects in the SLC11A2 gene 1
• Consider MRI of the liver to detect iron loading in patients with genetic disorders of iron metabolism 1

Treatment

• Treat patients with microcytic anemia due to pathogenic SLC11A2 defects with oral iron supplementation and/or erythropoietin (EPO) and/or erythrocyte transfusions, according to individual patient needs 1
• Monitor iron status closely to detect toxic iron loading at an early stage, and consider MRI of the liver to assess iron loading 1

From the Research

Causes of Microcytic Anemia

The causes of microcytic anemia can be categorized into acquired and congenital causes, and should be considered separately according to the age of the patient, risk factors, and coexisting signs and symptoms 2. Some of the main causes include:

• Iron deficiency anemia, which is the most common cause of microcytic anemia 3, 2, 4, 5
• Anemia of chronic disease, which is caused by a disturbance of iron utilization (functional iron deficiency) 4
• Thalassemia, a genetic disorder that affects the production of hemoglobin 3, 2, 5
• Sideroblastic anemia, a rare genetic disorder that affects the production of hemoglobin 2
• Sickle cell anemia, a genetic disorder that affects the shape of red blood cells 2

Risk Factors

Certain groups of people are at a higher risk of developing microcytic anemia, including:

• Infants, toddlers, premenopausal or pregnant women, and elderly people, who are at a higher risk of iron deficiency anemia 4
• Patients with chronic inflammatory conditions, such as chronic kidney disease, cirrhosis, or heart failure, who may have low iron stores due to inflammation 6
• Patients with gastrointestinal bleeding, menstruation, or pregnancy, who may experience disruptions in iron homeostasis 3

Diagnosis and Treatment

Diagnosing microcytic anemia involves measuring the mean corpuscular volume (MCV) and other laboratory parameters, such as serum ferritin, iron concentration, and transferrin saturation 3, 2, 5. Treatment depends on the underlying cause, but may include oral or intravenous iron supplementation for iron deficiency anemia 3, 2, 4, 6, and other treatments such as iron chelation for thalassemia 2.