Normal RDW Values in a Complete Blood Count
Normal RDW (Red Cell Distribution Width) is generally ≤14.0%, which represents the 95th percentile in reference populations, with typical laboratory ranges spanning 11.0-14.0%. 1
Standard Reference Range
- The normal RDW range is 11.0-14.0%, with values ≤14.0% considered within normal limits 1
- RDW 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 1
- A normal RDW indicates a homogeneous red cell population without significant anisocytosis (variation in red blood cell size) 1
Clinical Interpretation of Normal Values
When RDW is normal (≤14.0%):
- Combined with normal MCV: Suggests absence of early iron deficiency or vitamin deficiencies 1
- Combined with low MCV (microcytosis): A normal RDW with microcytosis helps differentiate thalassemia minor from iron deficiency anemia, as thalassemia typically presents with normal or only mildly elevated RDW while iron deficiency shows elevated RDW (>14.0%) 1
- Indicates uniform erythrocyte size: Reflects absence of significant heterogeneity in circulating red blood cells 1
Important Clinical Caveats
- Laboratory variation exists: RDW values can vary slightly between different laboratory instruments, so values should always be interpreted according to your specific laboratory's reference range 1
- Context matters: Even with normal RDW, if anemia is present, a minimum workup should include red blood cell indices, reticulocyte count, differential blood cell count, serum ferritin, transferrin saturation, and CRP concentration 1
- Clinical suspicion overrides normal values: If clinical suspicion for iron deficiency exists despite normal RDW, additional tests such as serum ferritin and transferrin saturation should be pursued 1
- Not used in isolation: RDW should always be interpreted alongside other hematologic parameters including hemoglobin, MCV, and other red cell indices 1
Historical Context
The mean RDW in normal male subjects has been documented as 11.3% in reference populations, confirming the lower end of the normal range 2