What is the likely diagnosis and recommended workup and treatment for a patient with microcytic hypochromic anemia (low hemoglobin, low MCV, low MCH, low MCHC), markedly elevated red cell distribution width, and thrombocytosis?

Microcytic Hypochromic Anemia with Elevated RDW and Thrombocytosis

Most Likely Diagnosis

Iron-deficiency anemia (IDA) is the most likely diagnosis given the severe microcytosis (MCV 65 fL), hypochromia (MCH 17.1 pg, MCHC 26.1 g/dL), markedly elevated RDW (20.1%), and reactive thrombocytosis (712 × 10³/µL). 1, 2

The markedly elevated RDW (20.1%) is particularly diagnostic, as it has 90–94% sensitivity for iron deficiency and helps distinguish IDA from thalassemia trait, where RDW is typically normal or only mildly elevated. 3, 4 The reactive thrombocytosis is a common finding in IDA due to shared regulatory pathways between erythropoiesis and thrombopoiesis.

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Recommended Diagnostic Workup

First-Line Iron Studies (Mandatory Before Treatment)

• Measure serum ferritin immediately—this is the single most specific test for iron deficiency. 1, 2

  • Ferritin < 15 µg/L is 99% specific for absolute iron deficiency 1, 2
  • Ferritin < 45 µg/L provides optimal sensitivity/specificity balance (92% specificity) and should trigger iron replacement 1, 2
  • Ferritin > 150 µg/L essentially excludes iron deficiency even with inflammation 2

• If ferritin is equivocal (45–150 µg/L) or inflammation is suspected, add transferrin saturation, total iron-binding capacity (TIBC), or soluble transferrin receptor. 1, 2

• Mean corpuscular hemoglobin (MCH) is more reliable than MCV because it is less affected by sample handling and remains abnormal in both absolute and functional iron deficiency. 2

Rule Out Thalassemia Trait

• Order hemoglobin electrophoresis if iron studies are normal or if MCV is disproportionately low relative to anemia severity. 1, 2

  • In β-thalassemia trait, MCV is typically < 70 fL with near-normal hemoglobin, and HbA₂ is elevated (> 3.5%) 1
  • The Mentzer index (MCV/RBC) can help: < 13 suggests thalassemia trait; > 13 suggests IDA 5
  • In this case, the RBC count is elevated (5.68 × 10⁶/µL) and Mentzer index is 11.4 (65/5.68), which favors thalassemia trait, but the markedly elevated RDW (20.1%) strongly favors IDA 3, 4, 5

• α-Thalassemia should be considered if hemoglobin electrophoresis is normal but microcytosis persists with normal iron studies; this requires molecular genetic testing. 6

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Investigation for Underlying Etiology

Assess Blood Loss Sources

• Obtain detailed menstrual history if the patient is female and of menstruating age—menorrhagia is the most common cause of IDA in adolescent and premenopausal women. 1, 2

• Perform urinalysis to exclude occult urinary blood loss. 2

• Gastrointestinal evaluation is warranted at any severity of anemia when iron deficiency is confirmed, with urgency increasing as anemia worsens because the risk of serious GI pathology (including malignancy) rises. 2

  • Test for Helicobacter pylori and celiac disease serology (tissue transglutaminase IgA with total IgA)—celiac disease is found in 3–5% of IDA cases and impairs iron absorption 2
  • Both upper and lower endoscopy are typically indicated in adults, especially men and postmenopausal women 2
  • In premenopausal women with menorrhagia, GI investigation is warranted if: (1) GI symptoms are present, (2) family history of GI pathology exists, or (3) anemia persists despite adequate iron replacement and menstrual management 2

Dietary and Medication Review

• Assess dietary iron intake and refer for nutritional counseling if insufficient. 1, 2

• Review medications that impair iron absorption (proton pump inhibitors, H₂ blockers, antacids) or cause GI bleeding (NSAIDs, anticoagulants). 2

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Treatment Recommendations

First-Line Oral Iron Therapy

• Initiate ferrous salts (ferrous sulfate, fumarate, or gluconate) once iron deficiency is confirmed—these are effective and least expensive. 1, 2

• Optimal absorption occurs on an empty stomach, but if gastrointestinal side effects (nausea, abdominal pain, constipation) occur, take with meals despite reduced absorption. 1, 2

• Co-administer 500 mg vitamin C or take with meat protein to enhance absorption. 1, 2

• Avoid concurrent calcium or high-fiber foods unless vitamin C is also provided. 1, 2

Expected Response and Monitoring

• Expect hemoglobin to rise ≥ 10 g/L within 2 weeks—this strongly confirms absolute iron deficiency and serves as both therapeutic trial and diagnostic confirmation. 1, 2

• Recheck complete blood count in 2 weeks to document response; if inadequate, reassess adherence, absorption, and ongoing blood loss. 1

Indications for Intravenous Iron

• Consider IV iron if:
  • Severe iron deficiency with intolerance to oral iron 1
  • Conditions impairing oral iron absorption (celiac disease, inflammatory bowel disease) 1, 2
  • Failure of iron stores to improve despite adequate oral supplementation 1, 2
  • Heart failure or pregnancy with iron deficiency 2

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Critical Pitfalls to Avoid

• Do not start iron therapy before confirming iron deficiency with ferritin—empiric treatment can mask thalassemia trait and delay appropriate genetic counseling. 1

• Do not accept a "normal" ferritin at face value if inflammation is present—ferritin is an acute-phase reactant and may be falsely elevated. 2

• Do not rely solely on MCV and MCH—their diagnostic sensitivity declines in chronic disease, thalassemia, and mixed nutrient deficiencies. 2

• Do not omit GI investigation in men or postmenopausal women, even with mild anemia, because colorectal cancer can present with any degree of iron-deficiency anemia. 2

• Do not pursue unnecessary GI workup when hemoglobin electrophoresis confirms thalassemia trait in patients with appropriate ethnic background and normal iron studies. 2

• Do not overlook coexisting IDA and thalassemia trait—7% of children with microcytic anemia have both conditions, and the combination produces more severe anemia than either alone. 5, 6