What does a Red Cell Distribution Width (RDW) of 11.4 indicate?

Interpreting an RDW of 11.4

An RDW of 11.4 is within the normal range, indicating uniform red blood cell size distribution without significant anisocytosis, suggesting absence of iron deficiency anemia or other common hematologic disorders that cause variation in red cell size. 1

Understanding RDW Values

• RDW (Red Cell Distribution Width) is calculated by dividing the standard deviation of red blood cell volume by MCV and multiplying by 100 to express the result as a percentage 1
• Normal RDW is generally considered to be less than or equal to 14.0%, which corresponds to the 95th percentile in reference populations 1
• Your value of 11.4% falls within the normal range (typically 11.0-14.0%), indicating homogeneous red cell population 1

Clinical Significance of Normal RDW

• A normal RDW suggests uniform size of circulating erythrocytes, indicating absence of significant anisocytosis 1
• When combined with normal MCV (Mean Corpuscular Volume), a normal RDW suggests absence of early iron deficiency or vitamin deficiencies 1
• In the context of microcytosis (low MCV), a normal RDW (≤14.0%) can help differentiate thalassemia minor from iron deficiency anemia 1

RDW in Differential Diagnosis

• When evaluating microcytic anemia, RDW helps distinguish between causes:
  • Iron deficiency anemia typically presents with elevated RDW (>14.0%) and low MCV 1, 2
  • Thalassemia minor typically presents with low MCV but normal or only mildly elevated RDW 1, 3
• In macrocytic anemias, RDW may be normal in approximately 31% of untreated pernicious anemia cases, contrary to common belief 4

Interpretation in Context

• RDW should always be interpreted alongside other hematologic parameters including hemoglobin, MCV, and other red cell indices 1
• A normal RDW with abnormal MCV still warrants investigation for potential underlying conditions 1
• 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 Implications

• Normal RDW suggests absence of active erythropoiesis in response to deficiency states 3
• If clinical suspicion for iron deficiency exists despite normal RDW, additional tests such as serum ferritin and transferrin saturation should be considered 1
• RDW has prognostic value beyond hematologic disorders - elevated values (not your case) are associated with increased mortality risk in cardiovascular disease and other conditions 5, 6

Monitoring Considerations

• If there are other abnormal hematologic parameters or clinical symptoms suggesting deficiency states, follow-up testing may be warranted despite normal RDW 1
• RDW values can vary slightly between different laboratory instruments, so values should be interpreted according to the specific laboratory's reference range 1