What is the most likely diagnosis and appropriate evaluation and management for a 40‑year‑old woman with hemoglobin 8 g/dL, hematocrit 29.2 %, microcytic anemia (MCV 68.9 fL, MCH 18.9 pg, MCHC 27.4 g/dL), elevated RDW 17.4 % and thrombocytosis (platelet count 479 ×10⁹/L)?

Most Likely Diagnosis: Iron Deficiency Anemia

This patient has iron deficiency anemia (IDA), and you should immediately check serum ferritin (target <45 μg/dL confirms IDA) and initiate oral iron supplementation while investigating the underlying cause of blood loss or malabsorption. 1, 2

Diagnostic Reasoning

The laboratory findings are classic for IDA:

• Severe microcytic anemia: MCV 68.9 fL (markedly reduced), MCH 18.9 pg, MCHC 27.4 g/dL
• Elevated RDW 17.4%: This has 94% sensitivity for iron deficiency and helps distinguish IDA from thalassemia trait (which typically has normal RDW) 3
• Reactive thrombocytosis (479 ×10⁹/L): Common in IDA due to shared precursor pathways between erythropoiesis and thrombopoiesis

The degree of microcytosis (MCV 68.9) with elevated RDW makes thalassemia trait unlikely, as thalassemia typically shows microcytosis disproportionate to anemia with normal or minimally elevated RDW 2, 3.

Immediate Diagnostic Work-Up

Order these tests now:

1. Serum ferritin - Most specific single test for IDA 2

   • <15 μg/dL = 99% specific for iron deficiency
   • <45 μg/dL = optimal sensitivity/specificity balance (92% specificity) 1, 2
   • If ferritin 45-100 μg/dL with inflammation suspected, add transferrin saturation

2. Consider checking vitamin B12 - The platelet/MCH ratio is 25.3 (479/18.9), which exceeds the 12.0 cutoff suggesting possible combined B12 and iron deficiency 4. However, given the severe microcytosis and elevated RDW, pure IDA is more likely.

Do NOT order Hb electrophoresis initially - Only needed if iron studies are normal and microcytosis persists, particularly in patients of Mediterranean, African, or Southeast Asian descent 2.

Investigate the Underlying Cause

For a 40-year-old woman, systematically evaluate:

1. Menstrual history - Heavy menstrual bleeding is the most common cause in premenopausal women 1

2. Gastrointestinal evaluation - Required if:

   • Postmenopausal status
   • Inadequate menstrual blood loss to explain severity
   • GI symptoms present
   • Failed response to iron therapy

   Per guidelines, consider bidirectional endoscopy (EGD and colonoscopy) to evaluate for:

   • Celiac disease (check tissue transglutaminase antibodies first)
   • H. pylori infection
   • Occult GI bleeding sources
   • Malabsorption 1, 2

3. Dietary assessment - Evaluate iron intake, vegetarian/vegan diet 1

Iron Replacement Strategy

Start oral iron immediately (don't wait for ferritin results if clinical picture is clear):

• Ferrous sulfate 325 mg daily (or ferrous fumarate/gluconate - all equally effective) 1
• Take on empty stomach when possible; with food if not tolerated
• Add vitamin C 500 mg to enhance absorption 1
• Expect Hb rise ≥10 g/L within 2 weeks - This response confirms IDA even if iron studies were equivocal 2

Consider IV iron if:

• Severe symptoms requiring rapid correction
• Intolerance to oral iron (nausea, constipation, abdominal pain)
• Malabsorption (celiac disease, inflammatory bowel disease)
• Ongoing blood loss exceeding oral replacement capacity 1

Common Pitfalls to Avoid

1. Don't assume "normal" ferritin rules out IDA - Ferritin is an acute phase reactant; levels up to 100 μg/dL can still represent iron deficiency in inflammatory states 1, 2

2. Don't stop at diagnosis - IDA in adults always requires investigation for the source, especially GI blood loss in this age group 2

3. Don't forget to replete iron stores - Continue iron for 3-6 months after Hb normalizes to rebuild stores 1

4. Don't overlook celiac disease - Check tissue transglutaminase antibodies, especially if refractory to oral iron 1

The thrombocytosis will resolve with iron repletion and requires no specific intervention 2.