Management of Mildly Elevated RDW
A mildly elevated RDW requires targeted laboratory workup to identify the underlying cause, with the minimum evaluation including complete blood count with MCV, reticulocyte count, serum ferritin, transferrin saturation, and CRP. 1
Initial Diagnostic Approach
The interpretation of elevated RDW must be done in conjunction with other hematologic parameters, particularly MCV, to guide the differential diagnosis and subsequent management. 1
Essential Laboratory Workup
When RDW is elevated above 14.0%, obtain the following tests: 1
- Complete blood count with MCV and hemoglobin
- Reticulocyte count (to assess erythropoietic activity)
- Serum ferritin (with inflammation-adjusted thresholds)
- Transferrin saturation
- C-reactive protein (CRP) (to assess for inflammation)
Interpretation Based on MCV Pattern
Microcytic Pattern (Low MCV + High RDW)
This combination strongly suggests iron deficiency anemia. 1 The elevated RDW reflects the heterogeneous red cell population as new microcytic cells are produced alongside older normocytic cells. 2
Diagnostic criteria for iron deficiency: 3
- Without inflammation: Serum ferritin <30 μg/L
- With inflammation present: Serum ferritin up to 100 μg/L may still indicate iron deficiency
Additional supportive findings for iron deficiency: 3
- Low serum iron
- Raised total iron-binding capacity
- Transferrin saturation <16%
- Microcytic hypochromic red cells on blood film
Important caveat: While thalassemia trait typically presents with normal or only mildly elevated RDW, nearly half of thalassemia cases can show increased RDW, limiting its specificity. 4 Therefore, hemoglobin studies are still needed when thalassemia is suspected despite elevated RDW.
Normocytic Pattern (Normal MCV + High RDW)
This pattern may indicate: 1
- Early iron deficiency (before MCV drops)
- Vitamin B12 or folate deficiency
- Hemolysis (correlate with reticulocyte count)
- Anemia of chronic disease
The elevated RDW in this context can help identify iron deficiency when microcytosis and macrocytosis coexist, resulting in a falsely normal MCV. 1
Mixed Picture (Ferritin 30-100 μg/L with inflammation)
When serum ferritin falls between 30-100 μg/L in the presence of inflammation, this suggests a combination of true iron deficiency and anemia of chronic disease. 3 In this scenario, the elevated RDW helps support the diagnosis of concurrent iron deficiency.
Management Based on Identified Cause
Iron Deficiency Confirmed
Treatment approach: 1
- Initiate iron supplementation (oral or intravenous based on severity and tolerance)
- Investigate potential sources of blood loss, particularly gastrointestinal causes
- Monitor response with repeat CBC and iron studies
Vitamin Deficiencies
Provide appropriate vitamin supplementation (B12 or folate) based on specific deficiency identified. 1
Inflammatory Conditions
Address the underlying inflammatory disorder as the primary management strategy. 1 The elevated RDW in inflammatory conditions reflects erythrocyte membrane injury and reduced deformability. 1
Clinical Pitfalls to Avoid
Do not rely on RDW alone for diagnosis. While RDW >17.1 strongly suggests iron deficiency anemia, sequential evaluation including iron and hemoglobin studies remains necessary. 4, 2
Remember that RDW values vary between laboratory instruments, so interpret according to your specific laboratory's reference range. 1
Even with clinical suspicion for iron deficiency despite only mildly elevated RDW, proceed with serum ferritin and transferrin saturation testing. 1
Prognostic Considerations
Beyond diagnostic utility, recognize that elevated RDW reflects deregulation of erythrocyte homeostasis involving impaired erythropoiesis and abnormal red blood cell survival, which may be attributed to oxidative stress, inflammation, poor nutritional status, or other metabolic abnormalities. 5 This broader significance underscores the importance of identifying and treating the underlying cause rather than viewing elevated RDW as an isolated laboratory finding.