Overview
- Red cell distribution width (RDW) is the amount of variation in red blood cell size. Cells may be relatively uniform in size and have a low RDW, or have a wide range of sizes and have a high RDW.
Normal Range
- 11 - 15%
Anisocytosis
- Elevated red cell distribution width (RDW) indicates that red blood cells are at a large range of sizes. This phenomenon is known as anisocytosis.
- In iron deficiency and megaloblastic anaemia, the RDW may elevate before the MCV becomes abnormal, and as such the RDW can be an early marker.
Causes of Anisocytosis
Predominantly Microcytic
- Iron deficiency anaemia
- Sideroblastic anaemia
Predominantly Normocytic
- Early iron deficiency anaemia
- Early megaloblastic anaemia
- Red cell fragmentation
- Immune haemolysis
- Sickle cell anaemia
- Sideroblastic anaemia
- Blood transfusion
Predominantly Macrocytic
- Megaloblastic anaemia (B12 / folate deficiency, drugs)
- Myelodysplastic syndrome
- Chronic liver disease
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------