Given a CBC that shows normocytic anemia (hemoglobin 10 g/dL, hematocrit 31.5 %, RBC 3.72 M/µL) with elevated red cell distribution width and neutrophil predominance, what is the most likely cause and what laboratory workup and treatment should be recommended?

Normocytic Anemia with Elevated RDW: Diagnostic Approach

This patient has normocytic anemia (MCV 84.9 fL) with a markedly elevated RDW (21.6%), which suggests either early iron deficiency anemia transitioning to microcytosis, mixed nutritional deficiencies (dimorphic anemia), or anemia of chronic disease with concurrent iron deficiency—you must immediately check serum ferritin, transferrin saturation, and assess for gastrointestinal blood loss.

Key Laboratory Findings Analysis

The CBC reveals several critical patterns:

• Anemia severity: Hemoglobin 10.0 g/dL with hematocrit 31.5% indicates moderate anemia
• RDW elevation: 21.6% (reference 11.5-16.0%) is markedly elevated, suggesting heterogeneous red cell populations
• Neutrophil predominance: 81.6% neutrophils (reference 37-80%) with absolute neutrophil count at upper normal (5.9 K/µL)
• Normal MCV: 84.9 fL indicates normocytic pattern currently, but elevated RDW suggests evolving process

Most Likely Differential Diagnoses

Primary Consideration: Iron Deficiency Anemia (Early/Transitional)

The elevated RDW with normocytic MCV represents a heterogeneous normocytic anemia pattern, which most commonly indicates iron deficiency in transition 1. As iron stores deplete, RDW rises before MCV drops, creating this exact laboratory picture.

Immediate workup required 1:

• Serum ferritin (absolute iron deficiency if <100 μg/L in general population, <200 μg/L if on dialysis)
• Transferrin saturation (iron deficiency if ≤20%)
• Consider reticulocyte count to assess bone marrow response

Secondary Consideration: Dimorphic Anemia

The markedly elevated RDW (21.6%) could indicate combined nutritional deficiencies (iron + B12/folate), creating populations of both microcytic and macrocytic cells that average to normocytic 2. This is particularly relevant given the severity of RDW elevation.

Tertiary Consideration: Anemia of Chronic Disease

The neutrophil predominance (81.6%) may suggest underlying inflammation or chronic disease 1, 3. However, anemia of chronic disease typically presents with normal or only mildly elevated RDW, making this less likely as the sole diagnosis.

Recommended Diagnostic Algorithm

Step 1: Iron Studies (First Priority)

• Ferritin: If <100 μg/L → absolute iron deficiency confirmed
• Transferrin saturation: If ≤20% → functional or absolute iron deficiency
• Interpretation caveat: Ferritin is an acute phase reactant; levels 100-300 μg/L may still represent iron deficiency if inflammation present 1

Step 2: If Iron Deficiency Confirmed

Gastrointestinal evaluation is mandatory 1:

• Upper endoscopy (esophagogastroduodenoscopy)
• Colonoscopy or CT colonography
• Rationale: GI blood loss is the most common cause of iron deficiency in adults, and dual pathology is common
• Check for medication use: aspirin, NSAIDs, anticoagulants that compound blood loss 1

Step 3: Additional Testing Based on Initial Results

If ferritin >100 μg/L but transferrin saturation ≤20%:

• Consider functional iron deficiency (anemia of chronic disease with inadequate iron mobilization)
• Evaluate for chronic kidney disease: serum creatinine, eGFR 1, 4
• Assess for chronic heart failure if clinically indicated 1

If iron studies normal:

• Vitamin B12 and folate levels (to evaluate for dimorphic anemia) 2
• Reticulocyte count to assess bone marrow response 4
• Peripheral blood smear review for hemolysis, dysplasia, or other morphologic abnormalities 3

Step 4: Evaluate Neutrophilia

The neutrophil predominance (81.6%) warrants assessment for:

• Underlying infection or inflammatory process
• Chronic disease contributing to anemia
• Medication effects (corticosteroids)
• Consider inflammatory markers (CRP, ESR) if chronic disease suspected

Treatment Recommendations

If Iron Deficiency Confirmed

Oral iron remains first-line 1:

• Ferrous sulfate 325 mg (65 mg elemental iron) daily to three times daily
• Take on empty stomach for optimal absorption
• Continue for 3-6 months after hemoglobin normalizes to replete stores

Parenteral iron indications 1:

• Intolerance to oral iron (common: nausea, constipation, abdominal pain)
• Malabsorption
• Ongoing blood loss exceeding replacement capacity
• Chronic kidney disease (especially if on dialysis) 1, 4

Address Underlying Cause

• Treat GI pathology if identified
• Discontinue or modify causative medications if possible
• Manage chronic kidney disease or heart failure per nephrology/cardiology 1

Critical Pitfalls to Avoid

1. Do not assume anemia of chronic disease without excluding iron deficiency: The elevated RDW strongly suggests iron deficiency, which is treatable 1

2. Do not skip GI evaluation if iron deficiency confirmed: Even in elderly or those with comorbidities, GI malignancy must be excluded unless patient is too frail for intervention 1

3. Do not interpret ferritin in isolation: In inflammatory states, ferritin can be falsely elevated; use transferrin saturation concurrently 1, 4

4. Do not transfuse unless symptomatic or hemodynamically unstable: Hemoglobin of 10.0 g/dL rarely requires transfusion in stable patients 3

5. Do not overlook combined deficiencies: RDW of 21.6% is markedly elevated and may indicate dimorphic anemia requiring both iron and B12/folate replacement 2