In a 50‑year‑old man with hemoglobin 12.9 g/dL, MCV 62 fL, MCH 21 pg, normal MCHC, RDW‑CV 17.4 % and eosinophils 9.8 %, what is the most likely cause and how should it be managed?

Microcytic Anemia with Eosinophilia: Iron Deficiency Anemia with Parasitic Evaluation

This 50-year-old man has iron deficiency anemia (IDA) requiring immediate gastrointestinal investigation to exclude malignancy, plus evaluation for parasitic infection given the marked eosinophilia.

Diagnosis

The laboratory findings definitively indicate iron deficiency anemia:

• Microcytosis (MCV 62 fL, well below normal) with hypochromia (MCH 21 pg) are hallmarks of IDA 1
• Normal MCHC (336 g/L) helps distinguish this from thalassemia, where MCHC is typically preserved or elevated 2, 3
• Elevated RDW-CV (17.4%) reflects the heterogeneous red cell population characteristic of iron deficiency 4, 5
• The hemoglobin of 12.9 g/dL meets WHO criteria for anemia in adult men (Hb <13 g/dL) 1

The eosinophilia (9.8%) is a critical additional finding that suggests parasitic infection, particularly hookworm, which is a well-recognized cause of IDA through chronic gastrointestinal blood loss 1.

Immediate Investigations Required

Confirm Iron Deficiency

• Serum ferritin is the most powerful diagnostic test; <12 μg/dL is diagnostic of iron deficiency 1
• In the presence of inflammation (which may be present), ferritin <30 μg/L confirms iron deficiency 1
• Transferrin saturation <15% supports the diagnosis 1

Gastrointestinal Evaluation (Mandatory)

All adult men with IDA require upper and lower GI investigation to exclude malignancy 1:

• Upper endoscopy with duodenal biopsies to screen for:

  • Gastric or esophageal cancer 1
  • Celiac disease (obtain tissue transglutaminase antibody if not already done) 1
  • Helicobacter pylori 1

• Colonoscopy (preferred over barium enema) to exclude:

  • Colorectal cancer or polyps 1
  • Angiodysplasia 1
  • Inflammatory bowel disease 1

Critical pitfall: Men with Hb <12 g/dL should be investigated urgently, as lower hemoglobin suggests more serious underlying disease 1. Do not delay investigation based on the "mild" degree of anemia.

Parasitic Evaluation

Given the eosinophilia, test for hookworm and other parasites 1:

• Stool examination for ova and parasites (three samples)
• Consider serologic testing for strongyloides and other helminths
• Travel and exposure history is essential

Management Algorithm

1. Iron Supplementation (Start Immediately)

All patients with IDA should receive iron supplementation to correct anemia and replenish stores 1:

• Oral iron is first-line therapy 1
• Continue for 3-6 months after hemoglobin normalizes to replenish stores 1
• Parenteral iron if oral preparations are not tolerated 1

2. Blood Transfusion Criteria

Reserve transfusions for patients with or at risk of cardiovascular instability 1:

• Not indicated in this stable patient with Hb 12.9 g/dL 1
• Consider if Hb drops to <7-8 g/dL or if symptomatic with cardiovascular compromise 1

3. Treat Underlying Cause

• Eradicate H. pylori if present 1
• Treat parasitic infection if identified (e.g., albendazole for hookworm) 1
• Address any GI malignancy found on endoscopic evaluation 1

4. Follow-Up Strategy

• Recheck hemoglobin after 3 weeks of iron therapy to confirm response 1
• If hemoglobin cannot be restored or maintained with iron therapy, further small bowel investigation (capsule endoscopy or enteroscopy) is indicated 1
• Dual pathology (bleeding sources in both upper and lower GI tract) occurs in 1-10% of patients, especially in older individuals 1

Critical Pitfalls to Avoid

• Do not attribute IDA solely to dietary deficiency in adult men—GI blood loss is the most common cause and malignancy must be excluded 1
• Do not ignore the eosinophilia—parasitic infection, particularly hookworm, is a recognized cause of IDA and requires specific treatment 1
• Faecal occult blood testing is of no benefit in investigating IDA and should not be used 1
• Do not stop at finding one lesion—dual pathology is common, so complete both upper and lower GI evaluation 1
• Normal MCHC does not exclude iron deficiency—the combination of low MCV, low MCH, and elevated RDW is diagnostic 2, 3, 4