What is the differential diagnosis for a patient with iron deficiency anemia (low Unbound Iron-Binding Capacity (UIBC), low ferritin), normal liver function (low Alanine Transaminase (ALT)), eosinophilia (high eosinophils), and thrombocytosis (high platelets)?

Differential Diagnosis: Iron Deficiency Anemia with Eosinophilia and Thrombocytosis

The most likely diagnosis is iron deficiency anemia secondary to chronic gastrointestinal blood loss from a parasitic infection or inflammatory bowel disease, with reactive thrombocytosis and eosinophilia pointing toward either helminthic infection or IBD with allergic/atopic features.

Primary Diagnostic Considerations

Iron Deficiency Anemia Pattern

• Low ferritin and low UIBC confirm absolute iron deficiency (ferritin <30 ng/mL in the absence of inflammation indicates true iron deficiency) 1, 2
• The low ALT suggests this is not primarily a hepatic or inflammatory process masking iron stores 3
• Gastrointestinal blood loss is the most common cause of iron deficiency in adults, requiring investigation of both upper and lower GI tract 4, 5

Eosinophilia + Thrombocytosis Pattern

This combination with iron deficiency strongly suggests:

1. Parasitic Infection (Helminthic)

• Hookworm infection is a classic cause of iron deficiency anemia with eosinophilia 4
• Other helminths (strongyloides, ascaris) cause chronic GI blood loss with marked eosinophilia
• Thrombocytosis occurs as a reactive phenomenon to chronic blood loss and inflammation 5

2. Inflammatory Bowel Disease (IBD)

• IBD affects 40-66% of patients with anemia, with iron deficiency being the predominant cause 3
• Eosinophilia can occur in IBD, particularly ulcerative colitis with concurrent allergic features
• Thrombocytosis is common in active IBD as an acute phase reactant 3
• The low ferritin (<30 ng/mL) without elevated inflammatory markers (low ALT) suggests either quiescent disease or pure iron deficiency 3, 2

3. Celiac Disease

• Causes iron malabsorption leading to deficiency 1
• Can present with eosinophilia (less common but documented)
• Thrombocytosis may occur with chronic malabsorption
• AGA recommends serologic testing for celiac disease in all patients with iron deficiency anemia 1

Recommended Diagnostic Algorithm

Immediate Laboratory Workup

• Complete iron panel: Confirm transferrin saturation <16% to verify iron deficiency 3, 2
• Inflammatory markers: CRP and ESR to assess for occult inflammation (ferritin interpretation depends on inflammatory state) 3
• Stool studies: Ova and parasites (×3), fecal occult blood testing 4
• Celiac serologies: Tissue transglutaminase IgA with total IgA 1
• H. pylori testing: Non-invasive testing recommended for iron deficiency anemia 1

Endoscopic Evaluation

• Bidirectional endoscopy is strongly recommended for iron deficiency anemia in adults 1
• Upper endoscopy with small bowel biopsies (even if celiac serology negative, given malabsorption risk) 1
• Colonoscopy to exclude colonic pathology, IBD, angiodysplasia 4
• Consider video capsule endoscopy if bidirectional endoscopy is negative and transfusion-dependent 1

Additional Considerations

• Bone marrow examination is NOT typically needed; peripheral markers are sufficient 2
• If eosinophilia persists without parasitic cause, consider eosinophilic gastroenteritis or hypereosinophilic syndrome
• Thrombocytosis >600,000 warrants evaluation for primary myeloproliferative disorder, but reactive thrombocytosis is far more likely with this constellation 5

Critical Pitfalls to Avoid

Ferritin Misinterpretation

• Do not dismiss iron deficiency if ferritin is 30-100 ng/mL in the presence of any inflammation 3, 2
• However, your patient has LOW ferritin with LOW ALT, making true iron deficiency highly likely 2

Incomplete GI Evaluation

• Do not treat empirically without investigating the source of iron loss in adults 4, 5
• Occult malignancy (gastric, colonic) can present with this exact pattern 1, 4

Missing Parasitic Infection

• Geographic history and dietary exposures are essential
• Multiple stool samples increase sensitivity for parasite detection 4

Treatment Approach (After Diagnosis)

• Treat underlying cause first (parasites, IBD, celiac disease) 3, 5
• Oral iron supplementation: Ferrous sulfate 325 mg daily or alternate-day dosing 5
• Intravenous iron if malabsorption confirmed (celiac, IBD, post-bariatric surgery) or oral intolerance 5, 6
• Monitor response with hemoglobin and ferritin at 4-8 weeks 5

The combination of eosinophilia with iron deficiency anemia should trigger immediate consideration of parasitic infection, particularly in endemic areas or with appropriate exposure history, while simultaneously pursuing standard iron deficiency workup including bidirectional endoscopy and celiac screening 1, 4, 5.