Microcytosis: Defination, Symptoms, Causes, Diagnosis and more
Microcytosis refers to red blood cells that are smaller than normal. You have microcytosis if your mean corpuscular volume (MCV) value on a blood test is less than 80 femtoliters (fL). Microcytosis may be a sign of microcytic anemia, a condition usually caused by iron deficiency.
Key Points:
- Microcytosis: Red blood cells smaller than normal (< 6 µm), with MCV < 80 fL.
- Causes of Microcytosis: Iron deficiency, thalassemia, congenital/acquired sideroblastic anemia, HbE/HbC, hyperthyroidism, heavy metal poisoning.
- Microcytic RBCs: Smaller than 6 µm, retain central pallor, often associated with iron deficiency anemia.
- Associated with Anemia: Microcytosis is often a sign of microcytic anemia, caused by insufficient hemoglobin.
- Symptoms: Fatigue, pallor, shortness of breath, rapid heartbeat, pica (if iron deficient).
- Diagnosis: Complete blood count (CBC), peripheral blood smear, reticulocyte count, RDW, iron levels, ferritin, and TIBC.
- Testing Errors: Microcytic RBCs may be miscounted as platelets in automated counters, leading to inaccurate results.
Microcytosis associated with congenital or acquired portosystemic shunt is attributed to impaired iron metabolism, although the exact mechanism is unknown.
- Extreme microcytosis in a patient with iron deficiency and suspected thalassemic trait. VMC 47
- Microcytic RBCs are 6 microns or less in diameter. The mean corpuscular volume is usually less than 80 fL, although the normal range varies slightly among laboratories and age groups. Unlike spherocytes, which also have a reduced diameter, microcytes retain their central pallor. In iron deficiency microcytosis, central pallor increases (greater than 1/3 of the cell diameter).
- Impedance counters may erroneously count markedly microcytic RBCs as platelets, leading to a falsely elevated platelet count. Most of the RBCs in this image are also hypochromic.
What is Microcytosis?
Microcytosis means that your red blood cells are smaller than normal. This is a description, not an official diagnosis. You may know you have microcytosis after a routine blood test, called a complete blood count (CBC). A CBC is a test that provides information about your health by evaluating your blood cells.
| Condition | Cells Size | Mean Corpuscular Volume (MCV) | Description |
|---|---|---|---|
| Normal RBC Size (Normocytic) | 6-8 µm | 80–100 fL | RBCs have a normal size. |
| Microcytosis | < 6 µm | < 80 fL | RBCs are smaller than normal, often seen in conditions like iron deficiency anemia or thalassemia. |
| Macrocytosis | > 8 µm | > 100 fL | RBCs are larger than normal, often associated with vitamin B12 or folate deficiency, liver disease, or alcohol abuse. |
What is Microcytic Anemia?
Microcytic anemia occurs when red blood cells are smaller than normal because they do not have enough hemoglobin. Hemoglobin is a protein in red blood cells that helps red blood cells carry oxygen throughout the body. Doctors treat microcytic anemia by identifying and treating the condition that causes it.
Symptoms of Microcytosis:
Often there are no symptoms and the only sign of microcytosis is a low MCV value.
When symptoms do occur, they are the same as in microcytic anemia. They include:
- Fatigue.
- Palor.
- Difficulty breathing.
- Rapid heartbeat.
- Pica (occurs only if microcytosis is caused by iron deficiency).
You may also experience symptoms associated with the cause of microcytosis.
Causes of Microcytosis:
- Thalassaemia
- HbE/HbC
- Congenital sideroblastic anaemia
- Iron deficiency
- MDS, particularly if associated with acquired HbH disease
- Hyperthyroidism
- Acquired sideroblastic anaemia
- Heavy metal poisoning
Diagnosis and Tests:
Providers use these blood tests to diagnose microcytic anemia:
- Complete blood count (CBC): This test gives providers information about hemoglobin levels and appearances of the blood.
- Peripheral blood smear: Providers use this test to examine blood cells. While some blood tests examine blood cells with a machine, providers perform the test by examining blood cells under a microscope.
- Reticulocyte count: This test measures the number of immature red blood cells (reticulocytes) in the bone marrow. A reticulocyte count can tell your doctor whether your bone marrow is producing enough healthy red blood cells.
- Red Blood Cell Distribution Width (RDW): RDW measures the variation in the size of red blood cells. It is a value included in a complete blood count. Red blood cells are generally the same size. A large variation in cell size (aniocytosis) can suggest certain conditions.
- Iron Levels: Low iron levels are a sign of iron deficiency anemia.
- Ferritin Levels: Ferritin is a protein found in cells that stores iron. Ferritin levels are useful in determining how much iron is available in the body.
- Total Iron Binding Capacity (TIBC): In combination with iron and ferritin levels, this test helps in the diagnosis of iron deficiency. These levels also help identify anemia due to chronic disease or inflammation.
