Diagnostic Approach to Neutropenia with Relative Lymphocytosis and Elevated RDW

Primary Concern: Elevated RDW Analysis

• The Centers for Disease Control and Prevention recommends that an elevated RDW (>14.0%) indicates heterogeneous red blood cell populations, which strongly suggests iron deficiency anemia rather than thalassemia trait or chronic disease 1
• Iron deficiency typically presents with RDW >14.0% due to the presence of both older normal-sized cells and newer microcytic cells being produced under iron-deficient conditions, as suggested by the MMWR Recommendations and Reports 1

Essential Initial Laboratory Workup for RDW Elevation

• Serum ferritin (<30 μg/L confirms iron deficiency; <100 μg/L if inflammation present) is the crucial first test, according to Praxis Medical Insights 2
• Complete blood count with MCV to assess for microcytosis (low MCV + high RDW = iron deficiency; low MCV + low RDW = thalassemia), as recommended by the MMWR Recommendations and Reports and Praxis Medical Insights 1, 2

Secondary Concern: Neutrophil/Lymphocyte Pattern

• Recent or resolving acute viral illness can cause a neutrophil/lymphocyte pattern with lymphocyte predominance, as indicated by the MMWR Recommendations and Reports 1
• Early autoimmune disease (SLE, rheumatoid arthritis) can cause both neutropenia and elevated RDW through chronic inflammation and oxidative stress, according to Cell Death and Disease 4

Recommended Diagnostic Algorithm

• Measure serum ferritin, transferrin saturation, and CRP simultaneously to confirm iron status, as suggested by Praxis Medical Insights 2
• If ferritin confirms iron deficiency, investigate the source (dietary inadequacy vs. occult blood loss), according to Praxis Medical Insights 2

Treatment Approach

• Initiate oral iron supplementation (ferrous sulfate 325 mg daily or equivalent elemental iron 65 mg daily) if iron deficiency is confirmed, as recommended by Praxis Medical Insights 2
• Recheck CBC in 4-6 weeks to confirm reticulocyte response and declining RDW, as suggested by Praxis Medical Insights 2
• Do not ignore persistent neutropenia—if it persists after iron repletion, pursue autoimmune or infectious workup, according to Cell Death and Disease 4