RDW — Red Cell Distribution Width
RDW (Red Cell Distribution Width) is a parameter reflecting the degree of variation (anisocytosis) in red blood cell sizes. RDW is measured as a percentage (%) and indicates how much the blood cells differ in volume.
The higher the RDW, the greater the difference between the smallest and largest erythrocytes. This is an important marker in diagnosing anemias and other hematopoietic disorders.
Normal RDW values:
- Adults: 11.5–14.5%
- Children: 11.6–14.8%
Why RDW is ordered:
- To diagnose and differentiate various types of anemia
- To assess treatment effectiveness
- For early detection of iron, vitamin B12, or folic acid deficiencies
Elevated RDW may indicate:
- Iron deficiency anemia
- Anemia due to vitamin B12 or folic acid deficiency
- Hemolytic anemias (red blood cell destruction)
- After massive blood loss or blood transfusions
- Liver diseases, alcoholism
Low or normal RDW in pathologies:
- Thalassemia
- Chronic diseases (without pronounced anisocytosis)
Features:
- RDW is important in combination with MCV (mean corpuscular volume). For example, low MCV combined with high RDW is typical for iron deficiency anemia.
- Sharp fluctuations in RDW may be an early sign of disrupted erythropoiesis (red blood cell production).
Preparation for the test:
- Blood is drawn from a finger or vein in the morning, fasting
- Avoid alcohol, heavy physical and emotional stress before the test