The role of red blood cells and their normal shape
Red blood cells, also known as erythrocytes, are essential for life. Their primary function is to transport oxygen from the lungs to the body's tissues and return carbon dioxide to the lungs. To perform this efficiently, healthy red blood cells are uniform in size and shape, resembling a biconcave disk—a flattened, doughnut-like shape with an indentation in the center. This unique design maximizes their surface area, allowing for optimal gas exchange and flexibility to squeeze through tiny capillaries.
When red blood cells deviate from this standard biconcave shape, they are considered atypical. This abnormality, termed poikilocytosis, is a significant indicator of an underlying medical issue. A blood smear analysis, which is a microscopic examination of a blood sample, is used to identify these unusual cell shapes and can provide valuable clues for a diagnosis.
Inherited causes of atypical red blood cells
Several genetic conditions can interfere with the formation of red blood cells, leading to permanently atypical shapes. These are often present from birth and are due to mutations that affect the proteins or enzymes involved in cell development.
Sickle cell disease
One of the most well-known causes of atypical red blood cells is sickle cell disease, an inherited blood disorder.
- Cause: A mutation in the hemoglobin gene leads to the production of abnormal hemoglobin (hemoglobin S).
- Cell shape: Under low oxygen conditions, red blood cells with hemoglobin S become rigid and take on a characteristic sickle or crescent shape.
- Impact: These sickle-shaped cells can get stuck in blood vessels, blocking blood flow and causing pain, organ damage, and serious complications.
Thalassemia
Thalassemia is another inherited blood disorder that results in the body producing less hemoglobin than normal.
- Cause: Genetic defects affect the production of hemoglobin chains.
- Cell shape: The red blood cells often appear smaller (microcytic) and paler (hypochromic) and can take on a distinctive target cell appearance, known as codocytes.
Hereditary spherocytosis and elliptocytosis
These conditions affect the structural integrity of the red blood cell membrane.
- Hereditary spherocytosis: The red blood cells lack some of the membrane proteins, causing them to become spherical (spherocytes) instead of biconcave disks.
- Hereditary elliptocytosis: A mutation affects the proteins of the red blood cell skeleton, causing the cells to be oval or elongated (elliptocytes).
Acquired causes of atypical red blood cells
In many cases, atypical red blood cells develop later in life due to acquired conditions. These can be related to nutritional deficiencies, systemic diseases, or exposure to certain toxins.
Nutritional deficiencies
Deficiencies in key nutrients required for red blood cell production are a common cause of abnormal cell morphology.
- Iron-deficiency anemia: The body needs iron to produce hemoglobin. A lack of iron results in smaller, paler red blood cells (microcytes) and can cause elongated or pencil-shaped cells known as elliptocytes.
- Megaloblastic anemia: This is caused by deficiencies in vitamin B12 or folate. It results in the production of larger-than-normal red blood cells (megalocytes) that are immature.
Liver and kidney diseases
Diseases affecting the liver and kidneys can disrupt red blood cell development and lead to misshapen cells.
- Liver disease: Atypical red blood cell shapes, including acanthocytes (spur cells) and target cells, can result from imbalances in blood lipids associated with severe liver disease.
- Kidney disease: Severe kidney disease can lead to the production of echinocytes (burr cells).
Other acquired conditions
Other factors can also contribute to atypical red blood cell formation.
- Autoimmune hemolytic anemia: The body's immune system mistakenly attacks and destroys red blood cells, causing irregularly shaped fragments known as schistocytes.
- Burns: Severe burns can damage red blood cells, causing fragmentation.
- Poisoning: Exposure to heavy metals like lead can cause basophilic stippling, where ribosomes and other remnants aggregate within the cells.
Atypical RBC types and their underlying causes
| Atypical RBC Type | Description | Common Underlying Causes | Potential Symptoms |
|---|---|---|---|
| Sickle Cells (Drepanocytes) | Crescent or sickle-shaped cells. | Sickle cell disease. | Pain crises, fatigue, jaundice. |
| Target Cells (Codocytes) | Red blood cells with a dark center and outer ring. | Thalassemia, liver disease, iron-deficiency anemia. | Mild to moderate anemia, fatigue. |
| Spherocytes | Abnormally spherical, lacking the central pale area. | Hereditary spherocytosis, autoimmune hemolytic anemia. | Jaundice, splenomegaly, anemia. |
| Elliptocytes (Ovalocytes) | Oval or egg-shaped cells. | Hereditary elliptocytosis, iron-deficiency anemia. | Mild or asymptomatic, though can cause anemia. |
| Acanthocytes (Spur Cells) | Cells with irregularly spaced, thorny projections. | Severe liver disease, McLeod syndrome, some anemias. | Often associated with underlying disease symptoms. |
| Echinocytes (Burr Cells) | Cells with short, evenly spaced projections. | Kidney disease, pyruvate kinase deficiency. | Anemia, fatigue related to underlying condition. |
| Schistocytes | Irregular, fragmented cells. | Hemolytic anemias, severe burns, disseminated intravascular coagulation (DIC). | Anemia, bruising, petechiae. |
The diagnostic process
When atypical red blood cells are found during a routine blood test, a doctor will likely perform further investigation. A crucial first step is a peripheral blood smear, where a lab technician examines the blood under a microscope. The technician can identify the specific type and proportion of abnormal red blood cells, providing a critical diagnostic clue. Depending on the results, additional tests may be ordered to pinpoint the exact cause, such as:
- Blood tests for iron, vitamin B12, and folate levels.
- Genetic testing for inherited disorders like sickle cell disease or thalassemia.
- Liver and kidney function tests to check for systemic disease.
- Bone marrow biopsy in severe cases or to investigate myelofibrosis.
Conclusion
Understanding why are red blood cells atypical is vital for diagnosing a wide range of underlying health conditions, from inherited disorders to acquired illnesses. The appearance of abnormally shaped red blood cells, known as poikilocytosis, is not a disease in itself but a signpost pointing to a deeper issue. Correctly identifying the specific type of atypical cell and its cause is the key to effective treatment. If you have been informed of atypical red blood cells in a blood test, consulting with a healthcare professional is the next step toward a clear diagnosis and appropriate management plan.
For more information on hematology, visit the American Society of Hematology website.
