What is the most likely diagnosis for a patient with hemoglobin 13.3 g/dL, hematocrit 43.8 %, RBC count 5.60 ×10⁶/µL, MCV 78 fL, MCH 23.8 pg, MCHC 30.4 g/dL, RDW 16.6 % and how should this condition be evaluated and managed?

Microcytic Anemia with Elevated RDW: Iron Deficiency Anemia

This patient has iron deficiency anemia (IDA), evidenced by microcytosis (MCV 70-78 fL), hypochromia (MCH 21.0-23.8 pg, MCHC 30.0-30.4 g/dL), elevated RDW (16.2-16.6%), and elevated RBC count (5.42-5.60 ×10⁶/µL) despite borderline-low hemoglobin. 1, 2

Why This is Iron Deficiency Anemia

The combination of low MCV, low MCH, low MCHC, and elevated RDW is pathognomonic for iron deficiency. 1, 2 The bone marrow produces progressively smaller, more hypochromic red blood cells as iron stores deplete, creating a mixed population of normal-sized older cells and microcytic newer cells—this heterogeneity drives the elevated RDW. 1

• MCH is the most reliable marker for iron deficiency, with values of 21.0-23.8 pg (reference 26.6-33.0 pg) strongly indicating iron-deficient erythropoiesis. 1, 2
• The elevated RBC count (5.42-5.60 ×10⁶/µL) represents a compensatory response to tissue hypoxia, attempting to maintain oxygen delivery despite reduced hemoglobin per cell. 3
• The progressive worsening between the two time points (MCV declining from 78 to 70 fL, MCH from 23.8 to 21.0 pg, hemoglobin from 13.3 to 11.4 g/dL) confirms ongoing iron depletion. 1

Immediate Diagnostic Workup

Essential First-Line Tests

• Obtain serum ferritin and transferrin saturation immediately to confirm iron deficiency. 1, 2 Ferritin <30 μg/L confirms IDA without inflammation; transferrin saturation <15-16% supports the diagnosis and is less affected by inflammation than ferritin. 1, 2
• Measure C-reactive protein (CRP) to interpret ferritin accurately, because ferritin rises as an acute-phase reactant during inflammation. 1, 2 In the presence of inflammation, ferritin <100 μg/L may still indicate iron deficiency. 1
• Order an absolute reticulocyte count to assess bone marrow response. 1 A low or inappropriately normal reticulocyte count in the setting of anemia indicates inadequate marrow response to red cell loss. 1

Critical Pitfall to Avoid

Do not assume thalassemia trait based solely on microcytosis and elevated RBC count. 2 While thalassemia trait can present with similar CBC findings, the low MCHC (30.0-30.4 g/dL) and elevated RDW (16.2-16.6%) strongly favor iron deficiency over thalassemia. 3 Thalassemia trait typically shows normal or near-normal MCHC and low-normal RDW due to uniform microcytosis. 3

Investigation for Underlying Cause

All adult patients with confirmed iron deficiency require investigation for the source of blood loss. 1

In Premenopausal Women

• Assess menstrual history for heavy or prolonged bleeding (menorrhagia). 1
• Evaluate dietary iron intake and absorption issues (celiac disease, inflammatory bowel disease, prior gastric surgery). 1

In Adult Men and Postmenopausal Women

• Gastrointestinal evaluation is mandatory to exclude malignancy, regardless of anemia severity. 1 This typically includes upper endoscopy and colonoscopy. 1
• Assess for occult gastrointestinal bleeding with fecal occult blood testing if endoscopy is delayed. 1

Additional Considerations

• Screen for malabsorption disorders (celiac disease serology, inflammatory bowel disease markers) when dietary intake appears adequate. 1
• Review medications that may cause gastrointestinal bleeding (NSAIDs, anticoagulants, antiplatelet agents). 1

Treatment Approach

Iron Supplementation

Iron supplementation is recommended in all patients when iron deficiency anemia is confirmed. 4, 1

• Oral iron (ferrous sulfate 325 mg three times daily) is first-line therapy for most patients. 5 This provides approximately 195 mg of elemental iron daily. 5
• Intravenous iron should be reserved for patients who cannot tolerate or absorb oral preparations, or when rapid repletion is needed. 1 Options include iron sucrose 200 mg over 2-5 minutes, administered 5 times within 14 days. 5
• Monitor iron status during treatment to assess response and detect potential iron overload. 1 Repeat CBC, ferritin, and transferrin saturation at 4-6 weeks. 1

Expected Response

• Reticulocytosis should occur within 5-10 days of initiating iron therapy, followed by hemoglobin increase of approximately 1 g/dL every 2-3 weeks. 5
• Continue iron supplementation for 3-6 months after hemoglobin normalizes to replenish iron stores. 1

Monitoring and Follow-Up

• Repeat CBC in 4-6 weeks to confirm hemoglobin response. 1 Failure to respond suggests ongoing blood loss, malabsorption, incorrect diagnosis, or non-adherence. 1
• If hemoglobin fails to increase by ≥1 g/dL after 4-6 weeks of adequate iron therapy, reassess for alternative diagnoses (anemia of chronic disease, thalassemia trait, sideroblastic anemia) or persistent blood loss. 1, 2
• Once the underlying cause is identified and treated, monitor CBC annually to detect recurrence. 1