In a patient with an elevated red blood cell count, low hemoglobin, low hematocrit, microcytosis, low mean corpuscular volume, low mean corpuscular hemoglobin, borderline elevated red cell distribution width, and mild leukocytosis with neutrophil predominance, what is the most likely cause of the anemia and what diagnostic work‑up and treatment should be pursued?

Microcytic Anemia with Elevated RBC Count: Iron Deficiency Anemia

This patient has iron deficiency anemia (IDA), and you should immediately confirm this with serum ferritin testing (target <45 μg/dL), then initiate iron supplementation while simultaneously investigating the source of iron loss, particularly gastrointestinal bleeding.

Understanding This Blood Picture

Your patient presents with a classic microcytic, hypochromic anemia pattern:

• Microcytosis: MCV 60.33 fL (severely reduced)
• Hypochromia: MCH 19.17 pg (severely reduced)
• Elevated RBC count: 6.00 million/cumm (compensatory erythropoiesis)
• Low hemoglobin: 11.5 g/dL
• Borderline elevated RDW: 14.6% (indicating anisocytosis)

The elevated RBC count with low MCV creates a distinctive pattern. While thalassemia trait classically presents with microcytosis and elevated RBC count, the severely reduced MCV (60.33 fL) and elevated RDW strongly favor iron deficiency over thalassemia 1. In thalassemia trait, RDW is typically normal or only mildly elevated, whereas IDA characteristically shows increased RDW due to heterogeneous red cell populations 2, 3.

Diagnostic Algorithm

Step 1: Confirm Iron Deficiency

Serum ferritin is your single most useful test 4. Order:

• Serum ferritin (diagnostic if <15 μg/L; suggestive if <45 μg/L) 5, 4
• Transferrin saturation (low in IDA)
• Total iron-binding capacity (elevated in IDA)

Critical caveat: Ferritin is an acute phase reactant. If inflammatory conditions are suspected and ferritin is 45-100 μg/dL, add transferrin saturation or soluble transferrin receptor to confirm true iron deficiency 5.

Step 2: Identify the Source of Iron Loss

In adults, IDA is presumed to be from blood loss until proven otherwise 4. The gastrointestinal tract is the most common source, and gastrointestinal malignancy must be considered 1.

Pursue:

• Detailed menstrual history (if premenopausal woman)
• Dietary assessment for inadequate iron intake
• Medication review (NSAIDs, anticoagulants, aspirin)
• Testing for H. pylori (impairs iron absorption) 5
• Gastrointestinal evaluation: Bidirectional endoscopy (upper and lower) is indicated for unexplained IDA, particularly with hemoglobin <110 g/L in men or <100 g/L in non-menstruating women 4

Step 3: Rule Out Thalassemia Trait

If iron studies are normal or equivocal despite the microcytosis:

• Hemoglobin electrophoresis to detect beta-thalassemia trait (elevated HbA2) 1
• Consider alpha-thalassemia genetic testing if appropriate ethnic background and normal HbA2

The severely low MCV (60.33 fL) with elevated RDW makes thalassemia less likely, but this must be excluded definitively 6, 2.

Treatment Approach

Iron Repletion

Start oral iron supplementation immediately while diagnostic workup proceeds 5:

• Ferrous sulfate, ferrous fumarate, or ferrous gluconate (least expensive, reasonable first choice) 5
• Dosing: Take on empty stomach for optimal absorption; if not tolerated, take with meals containing meat protein 5
• Add vitamin C 500 mg to enhance absorption 5
• Monitor response: Hemoglobin should rise ≥10 g/L within 2 weeks, which confirms iron deficiency even if initial iron studies were equivocal 4

When to Use IV Iron

Consider intravenous iron if 5:

• Oral iron intolerance (nausea, abdominal pain, constipation)
• Malabsorption conditions (celiac disease, inflammatory bowel disease)
• Severe iron deficiency requiring rapid repletion
• Inadequate response to oral iron after appropriate trial

Key Clinical Pitfalls

1. Don't assume thalassemia based solely on elevated RBC count: The severely reduced MCV with elevated RDW points to IDA 2, 3

2. Don't miss occult GI bleeding: This degree of microcytosis in an adult warrants GI investigation unless another clear source is identified 4, 1

3. Don't rely on RDW alone: While elevated RDW favors IDA over thalassemia, there is significant overlap—almost half of thalassemia cases can have elevated RDW 3

4. Don't forget to replete iron stores: Treatment must continue beyond hemoglobin normalization to restore ferritin levels 7

5. Watch for false-normal ferritin: In patients with concurrent inflammation, infection, or liver disease, ferritin may appear normal despite true iron deficiency 5, 4

The mild neutrophilia (absolute neutrophils 7.68) may represent reactive changes from chronic blood loss or inflammation but does not alter the primary diagnostic approach to the anemia.