An alarming Red Cell Distribution Width (RDW) count is any value that falls outside the normal reference range, which is typically between 11% and 14%. When RDW values are either below 11% or above 14%, it indicates that the red blood cells vary significantly in size, suggesting a potential underlying health issue that warrants further investigation.
Understanding RDW
RDW stands for Red Cell Distribution Width, a measurement included in a standard complete blood count (CBC). It indicates the variation in the size and volume of your red blood cells (erythrocytes). Healthy red blood cells are generally uniform in size. A high RDW means there's a greater variation in cell sizes (a condition known as anisocytosis), while a low RDW means the red blood cells are more uniform than usual, though this is less commonly a standalone concern.
Normal vs. Alarming RDW Ranges
The reference range for RDW can vary slightly between laboratories, but generally, the alarming thresholds are defined as follows:
| RDW Category | Percentage Range (Approximate) | Interpretation |
|---|---|---|
| Normal | 11% to 14% | Red blood cells are largely uniform in size. |
| Alarming | Below 11% or Above 14% | Significant variation in red blood cell size, indicating a potential health issue. |
What an Alarming RDW May Indicate
An alarming RDW count is not a diagnosis in itself but rather a strong indicator that further diagnostic steps are needed to determine the root cause. It's crucial for healthcare providers to evaluate RDW results in conjunction with other components of the complete blood count, such as mean corpuscular volume (MCV), hemoglobin, and hematocrit levels.
High RDW (RDW-CV > 14%)
A higher-than-normal RDW suggests that new red blood cells are either larger or smaller than existing ones. This can be an early sign of various conditions, even before anemia fully develops or other blood parameters become abnormal. Common causes of high RDW include:
- Nutritional Deficiencies:
- Iron Deficiency Anemia: Often characterized by smaller red blood cells (microcytic), leading to a high RDW. Learn more about iron deficiency anemia.
- Vitamin B12 or Folate Deficiency Anemia: Typically involves larger red blood cells (macrocytic), which also results in a high RDW. Explore folate deficiency.
- Anemia of Chronic Disease: Conditions like kidney disease, liver disease, chronic inflammation, or certain cancers can impact red blood cell production.
- Hemolytic Anemia: Conditions where red blood cells are prematurely destroyed.
- Myelodysplastic Syndromes: A group of disorders caused by poorly formed or dysfunctional blood cells.
- Thalassemia: While sometimes associated with normal RDW, certain forms can show a slightly elevated RDW.
Low RDW (RDW-CV < 11%)
While "alarming" in the sense that it's outside the normal range, a low RDW is less commonly a primary clinical concern compared to a high RDW. It indicates that the red blood cells are exceptionally uniform in size.
- This finding alone is rarely indicative of a serious underlying condition.
- It typically means the red blood cell population is very homogeneous.
- When a low RDW is present, healthcare providers will usually focus on other blood parameters to assess overall health, as a low RDW often holds less diagnostic weight.
Next Steps After an Alarming RDW Count
If your RDW count is alarming, your healthcare provider will likely recommend:
- Reviewing Other Blood Tests: Analyzing other CBC parameters (MCV, MCH, MCHC, hemoglobin, hematocrit) to identify specific patterns of red blood cell changes.
- Clinical Evaluation: Taking into account your symptoms, medical history, and physical examination.
- Further Diagnostic Tests: Depending on the suspected cause, additional tests may include:
- Iron studies (ferritin, iron, total iron-binding capacity).
- Vitamin B12 and folate levels.
- Tests for inflammatory markers.
- Bone marrow examination (in rare cases).
It is essential to consult with a healthcare professional to interpret your RDW results and discuss any necessary follow-up actions.
