“Aniso” in a blood test refers to anisocytosis, a condition where a person’s red blood cells are of unequal size. While red blood cells typically maintain a relatively uniform size, significant variations can indicate underlying health concerns. Understanding this variation is important because red blood cells play a central role in delivering oxygen throughout the body.
Understanding Anisocytosis
Normally, red blood cells, also known as erythrocytes, are disc-shaped and generally maintain a consistent size to efficiently perform their function. Their primary role involves transporting oxygen from the lungs to the body’s tissues and carrying carbon dioxide back to the lungs for exhalation.
When red blood cells differ significantly in size, it can affect their ability to transport oxygen effectively, potentially leading to symptoms like fatigue or shortness of breath. This variation is not a condition in itself but rather a sign that an underlying issue might be impacting red blood cell production or maturation. The presence of both smaller (microcytic) and larger (macrocytic) cells contributes to this size disparity.
Measuring Anisocytosis: Red Cell Distribution Width (RDW)
The extent of anisocytosis is precisely measured in a blood test through a parameter called Red Cell Distribution Width (RDW). This measurement is a standard component of a complete blood count (CBC), a routine blood test that provides detailed information about various blood cell types.
The RDW is typically reported as RDW-CV (coefficient of variation), which is expressed as a percentage and reflects the width of the red blood cell volume curve. Another less common measurement is RDW-SD, which represents the standard deviation of red blood cell volume in femtoliters (fL). A higher RDW-CV indicates a greater degree of size variability among the red blood cells, signifying anisocytosis.
Interpreting Your RDW Results
A normal RDW value indicates that your red blood cells are relatively uniform in size, typically falling within a range of 11.5% to 14.5% or 15.4% for RDW-CV, though specific ranges can vary slightly by laboratory. A result within this normal range generally suggests consistent red blood cell production. Even with a normal RDW, however, other red blood cell indices might be abnormal, suggesting an underlying condition.
A high RDW signifies a significant variation in red blood cell sizes. This elevated RDW can be an early indicator of certain health conditions, sometimes even before other blood parameters, like hemoglobin levels, show abnormalities. Conversely, a low RDW is rare and typically not a cause for concern on its own, generally indicating a very uniform population of red blood cells.
Conditions Associated with Abnormal RDW
An elevated RDW can be associated with several medical conditions, primarily those affecting red blood cell production or lifespan. Iron deficiency anemia is a common cause, often presenting with a high RDW and typically smaller red blood cells (low MCV). This occurs because the body struggles to produce healthy, uniform red blood cells without sufficient iron.
Deficiencies in vitamin B12 or folate can also lead to an elevated RDW, often resulting in abnormally large red blood cells (high MCV). Thalassemia, a group of genetic blood disorders, can sometimes be associated with a normal RDW despite having smaller red blood cells, which helps differentiate it from iron deficiency.
Chronic diseases, such as kidney disease, liver disease, and heart disease, can also contribute to a high RDW due to their impact on red blood cell production or survival. Myelodysplastic syndromes, a group of bone marrow disorders, are another potential cause, as they involve abnormal production of blood cells, leading to size variation. Additionally, recent blood transfusions can temporarily increase RDW as the recipient’s blood mixes with donor cells of varying sizes.
Next Steps After an Abnormal RDW Result
An abnormal RDW result on its own is not a definitive diagnosis; rather, it serves as an indicator that warrants further medical evaluation. A healthcare provider will consider the RDW result in conjunction with other parameters from a complete blood count, such as Mean Corpuscular Volume (MCV), Mean Corpuscular Hemoglobin (MCH), and hemoglobin levels. These additional measurements help to narrow down the potential causes of the red blood cell size variation.
The doctor will also take into account the patient’s symptoms, medical history, and any other relevant clinical information. Based on this comprehensive assessment, further diagnostic tests may be recommended to identify the underlying condition. These might include specific vitamin level tests, iron studies, or other specialized investigations. It is important to avoid self-diagnosing and instead seek professional medical advice for proper interpretation and management of an abnormal RDW result.