What is the diagnosis and best initial management for a patient with serum iron 18 µg/dL, transferrin saturation 4 %, ferritin 9 ng/mL, hemoglobin 9.6 g/dL, hematocrit 33 %, mean corpuscular volume 70 fL, mean corpuscular hemoglobin 20.4 pg, red cell distribution width 16.8 %, and platelet count 493 ×10⁹/L?

Diagnosis: Severe Iron Deficiency Anemia

This patient has severe iron deficiency anemia requiring immediate oral iron supplementation and urgent gastrointestinal investigation to exclude occult malignancy.

Diagnostic Confirmation

The laboratory profile unequivocally confirms iron deficiency anemia:

• Ferritin 9 ng/mL is far below the 15 µg/L threshold, providing 99% specificity for absolute iron deficiency 1
• Transferrin saturation of 4% is markedly below the 20% cutoff, decisively confirming iron deficiency 1
• MCV 70 fL and MCH 20.4 pg demonstrate classic microcytic hypochromic anemia 1
• RDW 16.8% is elevated (>14%), serving as an early and sensitive marker of iron deficiency 1, 2
• Hemoglobin 9.6 g/dL meets WHO criteria for anemia in women (<12 g/dL) 1
• Reactive thrombocytosis (platelets 493 ×10⁹/L) correlates with the severity of iron deficiency; serum iron and transferrin saturation show significant negative correlation with platelet count 3

No additional iron studies are necessary when this complete laboratory pattern is present 1.

Immediate Management

Iron Replacement Therapy

• Start oral elemental iron 100–200 mg daily immediately while diagnostic workup proceeds 1
• Continue therapy for at least 3–6 months after hemoglobin normalization to fully replenish iron stores, targeting ferritin >50 µg/L 1
• Switch to intravenous iron if oral iron is poorly tolerated, malabsorption is documented, or hemoglobin fails to improve despite adherence 1
• Expect hemoglobin to increase by 1–2 g/dL within 4–8 weeks of therapy 1

Mandatory Investigation for Blood Loss

• Bidirectional endoscopy (upper endoscopy plus colonoscopy) must be performed promptly because gastrointestinal bleeding—particularly from colorectal or gastric malignancy—is the presumptive source until proven otherwise in adults with iron deficiency anemia 1
• Do not delay endoscopic evaluation even though hemoglobin is ≥9.6 g/dL; investigation is indicated at any anemia level when iron deficiency is present 1
• Do not attribute severe iron deficiency solely to menstrual blood loss in perimenopausal adults; gastrointestinal pathology must still be investigated 1

Laboratory Monitoring

• Recheck CBC and iron parameters (ferritin, transferrin saturation) 4–8 weeks after starting therapy 1
• Hemoglobin should begin rising within 1–2 weeks of treatment 1
• Do not discontinue iron supplementation once hemoglobin normalizes; continue until ferritin >50 µg/L to prevent rapid recurrence 1

Differential Considerations

• Low ferritin effectively rules out anemia of chronic disease, which typically presents with ferritin >100 µg/L, low TIBC, and transferrin saturation <20% 1
• If microcytosis persists after iron repletion—or if the patient belongs to an at-risk ethnic group—order hemoglobin electrophoresis to exclude β-thalassemia trait 1
• Do not diagnose thalassemia trait without first correcting iron deficiency, as the two conditions can coexist and iron deficiency can mask electrophoretic findings 1

Critical Pitfalls to Avoid

• Gastrointestinal malignancy work-up should proceed in parallel with iron therapy, not sequentially; do not postpone endoscopy while awaiting response to iron 1
• The severity of anemia (hemoglobin 9.6 g/dL) does not reduce the urgency of malignancy investigation; mild anemia is not less indicative of serious underlying disease 1
• Iron stores must be fully restored (ferritin >50 µg/L) even after hemoglobin normalizes, or recurrence will be rapid 1
• In this patient with ferritin 9 ng/mL and transferrin saturation 4%, inflammation is not confounding the diagnosis; these values unequivocally indicate absolute iron deficiency regardless of inflammatory status 1