Published: 18 Jun 2025

ICD9: 285.9      ICD10: D64.9      ICD11: 3A00.Y

Microcytic anemia is a type of anemia characterized by red blood cells that are smaller than normal.
"Microcytic" refers to the smaller size of the red blood cells, and "anemia" refers to a deficiency in the number of red blood cells or the amount of hemoglobin in the blood, leading to reduced oxygen carrying capacity.

Here's a breakdown:

Microcytic: "Micro" means small, and "cytic" refers to cells. In this case, it means the red blood cells (RBCs), also called erythrocytes, are smaller than their normal size. Doctors measure the average size of the RBCs with a test called the Mean Corpuscular Volume (MCV). A low MCV indicates microcytosis. Normal MCV range is typically between 80-100 femtoliters (fL), but this may vary slightly by lab. A microcytic anemia would have an MCV significantly below this range.

Anemia: A condition in which you don't have enough healthy red blood cells to carry adequate oxygen to your body's tissues. This can result in fatigue, weakness, shortness of breath, pale skin, and other symptoms.

Causes of Microcytic Anemia:

The most common causes of microcytic anemia relate to a problem with hemoglobin production. Hemoglobin is the protein in red blood cells that carries oxygen. It contains iron. The main causes include:

Iron Deficiency Anemia (IDA): This is the most common cause worldwide. It occurs when the body doesn't have enough iron to produce hemoglobin. Causes of iron deficiency include:
Blood loss: Chronic blood loss, such as from heavy menstrual periods, gastrointestinal bleeding (ulcers, colon cancer, etc.), or frequent blood donation.
Inadequate iron intake: Diet lacking sufficient iron, especially common in infants, children, and pregnant women.
Malabsorption: Conditions that impair iron absorption in the gut, such as celiac disease, Crohn's disease, or gastric bypass surgery.
Increased iron requirements: Pregnancy and breastfeeding increase iron demands.

Thalassemia: A group of inherited blood disorders that affect the production of globin chains (alpha or beta) in hemoglobin. Different types of thalassemia can exist, with varying degrees of severity. The reduced globin production also leads to smaller red blood cells and anemia.

Anemia of Chronic Disease (sometimes, but less common): Also known as anemia of inflammation. This type of anemia is associated with long-term infections, inflammatory conditions (like rheumatoid arthritis), and chronic diseases (like kidney disease or cancer). While often normocytic (normal-sized red blood cells), it can sometimes be microcytic, particularly in cases of severe or prolonged inflammation. The inflammatory process can interfere with iron utilization and erythropoietin production.

Sideroblastic Anemia: A group of disorders in which the bone marrow produces ringed sideroblasts (abnormal red blood cell precursors with iron granules accumulating around the nucleus) instead of healthy red blood cells. The iron is present but cannot be incorporated into hemoglobin properly. Can be acquired (due to medications, toxins, or myelodysplastic syndromes) or inherited.

Lead Poisoning: Lead interferes with hemoglobin synthesis, leading to microcytic anemia.

Diagnosis:

Complete Blood Count (CBC): This test measures the number, size, and shape of red blood cells, as well as hemoglobin levels. A low MCV (mean corpuscular volume) is the key finding for microcytic anemia. Low hemoglobin and hematocrit confirm the presence of anemia.
Iron Studies: Ferritin, serum iron, total iron-binding capacity (TIBC), and transferrin saturation are used to evaluate iron stores in the body and help differentiate between iron deficiency anemia and other causes of microcytic anemia. Low ferritin is a strong indicator of iron deficiency.
Hemoglobin Electrophoresis: This test helps diagnose thalassemia by identifying abnormal hemoglobin types.
Bone Marrow Biopsy: May be necessary in some cases to further evaluate the cause of anemia, especially in cases of sideroblastic anemia or when other tests are inconclusive.

Treatment:

Treatment depends on the underlying cause:

Iron Deficiency Anemia: Iron supplementation (oral or intravenous) is the primary treatment. It's also important to address the underlying cause of iron deficiency, such as blood loss or malabsorption.
Thalassemia: Treatment varies depending on the severity of the condition. Mild cases may not require treatment. More severe cases may require blood transfusions, chelation therapy (to remove excess iron from the body due to transfusions), or even bone marrow transplantation.
Anemia of Chronic Disease: Treating the underlying chronic disease is the primary goal. Erythropoiesis-stimulating agents (ESAs) may be used in some cases to stimulate red blood cell production, but their use is carefully considered due to potential risks.
Sideroblastic Anemia: Treatment depends on the type and severity. Some forms may respond to vitamin B6 supplementation. Others may require blood transfusions, chelation therapy, or bone marrow transplantation.
Lead Poisoning: Chelation therapy is used to remove lead from the body.

In summary, microcytic anemia is a condition where the red blood cells are smaller than normal, often due to problems with hemoglobin production, most commonly iron deficiency. Accurate diagnosis and treatment of the underlying cause are essential to manage the condition effectively. It's important to consult with a healthcare professional for proper diagnosis and management of any type of anemia.