What is the appropriate management for an abnormal Red Cell Distribution Width (RDW)?

Management of Abnormal Red Cell Distribution Width (RDW)

The appropriate management for an abnormal Red Cell Distribution Width (RDW) requires identifying and treating the underlying cause, with particular focus on iron deficiency anemia when RDW is elevated, and considering thalassemia when RDW is normal with microcytosis.

Understanding RDW Values

• RDW 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 2
• RDW values can vary slightly between different laboratory instruments, so values should be interpreted according to the specific laboratory's reference range 2

Diagnostic Approach for Abnormal RDW

Elevated RDW (>14.0%)

• An elevated RDW indicates increased variation in red blood cell size (anisocytosis) 3
• When combined with low MCV (microcytosis), strongly suggests iron deficiency anemia 1, 2
• When combined with normal MCV, may indicate early iron deficiency, vitamin B12 or folate deficiency, or hemolysis 2
• Minimum workup should include complete blood count with MCV, reticulocyte count, serum ferritin, transferrin saturation, and CRP 2

Normal RDW with Abnormal MCV

• Normal RDW with low MCV (microcytosis) suggests thalassemia minor rather than iron deficiency anemia 1, 4
• This distinction is important as treatment approaches differ significantly 2
• In cases of suspected thalassemia, hemoglobin electrophoresis should be considered 1

Management Based on Underlying Cause

Iron Deficiency Anemia (Elevated RDW, Low MCV)

• Confirm diagnosis with serum ferritin (<30 μg/L in absence of inflammation, <100 μg/L with inflammation) 1, 2
• Initiate iron supplementation (oral or intravenous) 2
• Investigate potential sources of blood loss, particularly gastrointestinal causes 1
• For adult men and post-menopausal women with iron deficiency anemia, both upper and lower gastrointestinal endoscopy should be performed to exclude malignancy 1

Thalassemia Minor (Normal RDW, Low MCV)

• Confirm with hemoglobin electrophoresis 2
• No specific treatment is typically required for thalassemia minor 2
• Avoid unnecessary iron supplementation 2

Vitamin Deficiencies (Elevated RDW, Normal or High MCV)

• For B12 deficiency: parenteral or high-dose oral B12 supplementation 2
• For folate deficiency: oral folate supplementation 2
• Address underlying causes of malabsorption if present 1

Chronic Disease and Inflammation (Variable RDW)

• Treat the underlying inflammatory condition 2
• In cases of anemia of chronic disease with concurrent iron deficiency (ferritin 30-100 μg/L with inflammation), consider iron supplementation 1

Special Considerations

• RDW has emerged as a prognostic marker in various conditions including cardiovascular disease, with higher values associated with worse outcomes 5, 6
• In patients with chronic heart failure, elevated RDW is an independent risk marker and adds prognostic information 5
• Serial monitoring of RDW may be valuable in assessing response to treatment 2, 7

Common Pitfalls to Avoid

• Assuming iron deficiency based solely on microcytosis without checking RDW 1, 2
• Failing to investigate for gastrointestinal malignancy in adult men and post-menopausal women with iron deficiency anemia 1
• Overlooking the possibility of combined deficiencies (e.g., iron and B12), which may result in a normal MCV despite abnormal RDW 1, 2
• Attributing microcytosis to thalassemia in certain ethnic groups without laboratory confirmation 1