What does a Red Cell Distribution Width (RDW) of 12.0 mean?

Understanding a Red Cell Distribution Width (RDW) of 12.0

A Red Cell Distribution Width (RDW) of 12.0 is within the normal range, indicating uniformity in red blood cell size and suggesting the absence of conditions that cause significant variation in erythrocyte dimensions. 1

What is RDW?

• RDW is a calculation that measures the variation in size of red blood cells (erythrocytes) in a blood sample 1
• It is calculated by dividing the standard deviation of red blood cell volume by the mean corpuscular volume (MCV) and multiplying by 100 to express as a percentage: RDW (%) = {SD of red blood cell volume (fL)/MCV (fL)} x 100 1
• RDW is routinely reported as part of a complete blood count (CBC) 2

Normal RDW Values

• A normal RDW is generally considered to be 14.0% or less 1
• The value of 12.0% falls well within this normal range 1
• The normal range corresponds to the 95th percentile of RDW for the reference population in NHANES III 1
• The specific RDW value obtained may depend on the instrument used for measurement 1

Clinical Significance of a Normal RDW

• A normal RDW indicates uniformity in the size of red blood cells (minimal anisocytosis) 3
• It suggests absence of conditions that cause significant variation in red blood cell dimensions 1
• When RDW is normal (≤14.0%) and MCV is low, it may help differentiate thalassemia minor from iron deficiency anemia 1
• Normal RDW values are associated with better outcomes in various conditions compared to elevated values 4, 5

RDW in Diagnostic Algorithms

• RDW is often used in conjunction with MCV to differentiate various types of anemias 1
• In cases of microcytic anemia (low MCV):
  • If RDW is normal (≤14.0%), thalassemia minor is more likely 1
  • If RDW is elevated (>14.0%), iron deficiency anemia is more likely 1
• RDW can help identify mixed deficiency states that might otherwise be missed 1
• A high RDW can be an early indicator of iron deficiency, even before anemia develops 1

Limitations and Considerations

• RDW should be interpreted in context with other hematologic parameters and clinical information 1
• The value may be affected by certain medications, recent blood transfusions, or laboratory processing factors 1
• While your RDW is normal, other parameters such as hemoglobin, MCV, and serum ferritin should be considered for a complete hematologic assessment 1
• RDW values may vary slightly between different laboratory instruments and methods 1

When to Consider Further Evaluation

• Even with a normal RDW, if clinical symptoms of anemia are present, further investigation may be warranted 1
• If other CBC parameters are abnormal, additional testing may be needed despite a normal RDW 1
• In certain clinical contexts, monitoring RDW trends over time may provide more information than a single measurement 4