A high red cell distribution width means red blood cells vary a lot in size, often from iron, B12, or folate deficiency. See a doctor for testing.
Meaning
RDW measures variation in red blood cell size. Normal is about 11.5% to 14.5%.
Causes of high RDW
- Iron deficiency anemia.
- Vitamin B12 or folate deficiency.
- Mixed anemias.
- Liver disease.
- Recent blood transfusion.
- Hemolytic anemia.
Interpretation
Doctors look at RDW with MCV.
See a doctor
For follow up tests.
What RDW measures
Red cell distribution width (RDW) reports how much red blood cells vary in size (anisocytosis). The usual range is about 11.5 to 14.5 percent for RDW-CV, depending on the lab. A high RDW means the cells differ more in size.
- Iron deficiency anemia commonly gives high RDW with low MCV (small cells), and RDW often rises before hemoglobin falls.
- B12 or folate deficiency gives high RDW with large cells (high MCV).
- Mixed deficiencies can give a normal MCV but high RDW.
- Recent transfusion, hemolytic anemia, liver disease and myelodysplastic syndromes can raise RDW.
Interpretation and outlook
Large studies, such as a 2009 analysis in the Archives of Internal Medicine, linked higher RDW to higher risk of death and cardiovascular events, though it is a marker and not a cause. A doctor reads RDW with MCV, hemoglobin, ferritin, B12 and folate. Treatment targets the cause, such as iron or B12 replacement. See a doctor if fatigue, shortness of breath or pale skin accompany the result.
What RDW measures
Red cell distribution width measures variation in red blood cell size. Normal is about 11.5 to 14.5 percent. High RDW suggests mixed cell sizes, as in iron deficiency, B12 or folate deficiency, or recent transfusion.
Interpretation and outlook
It is read with MCV and hemoglobin. High RDW has also been linked in studies to cardiovascular risk. Follow up testing identifies the cause.
What RDW shows
Red cell distribution width (RDW) measures how much red blood cells vary in size. A typical range is 11.5 to 14.5 percent. A high RDW, called anisocytosis, means cells are of mixed sizes. It is part of a complete blood count and is read together with MCV.
Interpreting a high value
High RDW with low MCV suggests iron deficiency, while high RDW with high MCV points to B12 or folate deficiency. Mixed deficiencies can produce a normal MCV with high RDW. Recent transfusion, thalassemia, liver disease and chronic inflammation also raise RDW. Research links higher RDW to cardiovascular risk and mortality, but it is not a stand alone diagnostic test. Follow up tests include ferritin, B12, folate and a peripheral smear.
Based on data from MedlinePlus and the Mayo Clinic Laboratories
