Anisocytosis is primarily tested for by measuring the red blood cell distribution width (RDW). A high RDW indicates a significant variation in red blood cell size, which is characteristic of anisocytosis.
Understanding Red Blood Cell Distribution Width (RDW)
The RDW is a numerical measurement obtained as part of a complete blood count (CBC). It quantifies the variation in size (volume) of your red blood cells. A normal RDW suggests that the red blood cells are generally uniform in size, while an elevated RDW indicates anisocytosis, meaning there is a wider range of red blood cell sizes present.
How the Test is Performed
- Blood Sample Collection: A healthcare professional will collect a blood sample, usually from a vein in your arm.
- CBC Analysis: The blood sample is sent to a laboratory for analysis using an automated cell counter. This machine measures various parameters of the blood, including the RDW.
- RDW Measurement: The RDW is calculated statistically, typically expressed as a percentage.
- Interpretation: The RDW value is then compared to the normal reference range established by the laboratory. A value above the upper limit of the normal range indicates anisocytosis.
Interpreting the RDW Value
While an elevated RDW indicates anisocytosis, it doesn't reveal the underlying cause. Further investigations are usually required to determine the reason for the variation in red blood cell size. Possible causes include:
- Iron Deficiency Anemia: One of the most common causes.
- Vitamin B12 or Folate Deficiency: These deficiencies can lead to abnormal red blood cell development.
- Hemoglobinopathies: Such as sickle cell anemia or thalassemia.
- Transfusion: Receiving a blood transfusion can introduce red blood cells of different sizes.
- Myelodysplastic Syndromes (MDS): A group of bone marrow disorders.
RDW in Conjunction with Mean Corpuscular Volume (MCV)
The RDW is often interpreted in conjunction with the Mean Corpuscular Volume (MCV), which measures the average size of red blood cells. Together, these values can help narrow down the possible causes of anemia.
| MCV Result | RDW Result | Possible Explanation |
|---|---|---|
| Normal | High | Early iron deficiency, mixed deficiency (iron, B12, folate) |
| Low | High | Iron deficiency anemia, thalassemia minor |
| High | High | Vitamin B12 or folate deficiency |
| Normal | Normal | Normal or anemia of chronic disease |
In summary, testing for anisocytosis involves a simple blood test to determine the RDW. An elevated RDW signifies a variation in red blood cell size, prompting further investigation to identify the underlying cause.
