Cell Size Consistency
RDW measures how much variation there is in the size of your red blood cells. Healthy blood has cells that are all roughly the same size. A high RDW means you have a mix of big and small cells—your bone marrow is struggling to produce uniform cells, usually because of a nutritional deficiency.
What is Red Cell Distribution Width?
RDW quantifies the variation in red blood cell volume as a percentage. It's a powerful diagnostic tool when combined with MCV—it helps distinguish between different types of anemia.
↑ What High Red Cell Distribution Width Means
Your red cells are varying wildly in size (anisocytosis). This almost always means something is disrupting normal production—iron deficiency, B12 deficiency, or mixed causes.
Common symptoms:
Symptoms depend on underlying cause: fatigue, weakness, breathlessness if anemia
↓ What Low Red Cell Distribution Width Means
Not typically concerning. Uniformly sized cells are normal.
Common symptoms:
Not typically associated with symptoms
Why It Matters
When normal:
Early indicator of nutritional deficiencies
Helps differentiate types of anemia
Cardiovascular risk marker in emerging research
Monitors treatment response
Risks if abnormal:
High RDW: iron deficiency, B12/folate deficiency, mixed anemia, liver disease
Elevated RDW independently associated with higher cardiovascular mortality
What Can Cause Abnormal Levels?
Iron Deficiency
65% likelyAs iron drops, new red cells are smaller while old cells remain normal-sized, creating variation.
B12 or Folate Deficiency
50% likelyProduces larger-than-normal cells mixed with normal ones.
Recent Blood Transfusion
Donor cells are different size than your own.
Reticulocytosis
Young red cells (reticulocytes) are larger, increasing size variation during active recovery.
What You Can Do
Iron-rich and B12-rich balanced diet
Impact: Normalizes red cell production \u00B7 Timeline: 4-8 weeks
Folate from leafy greens, beans, fortified grains
Impact: Supports uniform cell production \u00B7 Timeline: 4-8 weeks
If lifestyle changes aren't enough:
Targeted supplementation based on which deficiency exists
Impact: Directly addresses production issue \u00B7 Timeline: 8-12 weeks
Recommended retest: 3 months
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