What is the most likely diagnosis and recommended treatment for a patient with hemoglobin 101 g/L, red blood cell count 3.92 ×10^12/L, mean corpuscular volume 82.6 fL, reticulocyte count 0.036, and ferritin 5.62 µg/L?

Iron Deficiency Anemia

This patient has iron deficiency anemia (IDA) and requires immediate iron replacement therapy, preferably with intravenous iron given the severely depleted ferritin level of 5.62 µg/L.

Diagnosis

The laboratory values definitively establish iron deficiency anemia:

• Hemoglobin 101 g/L (10.1 g/dL): Below normal range, confirming anemia
• MCV 82.6 fL: Low-normal to slightly microcytic, consistent with early iron deficiency
• Ferritin 5.62 µg/L: Severely depleted—diagnostic of absolute iron deficiency 1
• Reticulocyte count 0.036 (3.6%): Low reticulocyte index indicating inadequate bone marrow response to anemia 2

A ferritin <12 µg/L is diagnostic of iron deficiency with near 99% specificity 1. This patient's ferritin of 5.62 µg/L leaves no diagnostic uncertainty—iron stores are essentially absent.

The low-normal MCV (82.6 fL) rather than frank microcytosis (<80 fL) is common in early or evolving iron deficiency 2, 3. The morphologic classification shows this is microcytic anemia with low reticulocyte production, pointing directly to iron deficiency as the cause 2, 4.

Underlying Cause Investigation

All adult patients with confirmed IDA require gastrointestinal evaluation to exclude malignancy and identify the source of blood loss 1. The specific approach depends on patient demographics:

For Men and Postmenopausal Women:

• Upper endoscopy with small bowel biopsies (to exclude celiac disease, which occurs in 2-3% of IDA cases) 1
• Colonoscopy or CT colonography (dual pathology occurs in ~10% of cases) 1
• Both examinations are mandatory unless a clear non-GI cause is identified 1

For Premenopausal Women:

• Assess menstrual blood loss history
• If menorrhagia is present and no other concerning features, may defer GI investigation initially 3
• However, do not assume dietary deficiency alone—GI investigation still warranted if anemia persists despite treatment 1

Additional Workup:

• Celiac serology (anti-tissue transglutaminase antibodies) if endoscopy not immediately available 1
• Stool for occult blood
• Medication review: NSAIDs, aspirin, anticoagulants 1
• H. pylori testing 5

Treatment Strategy

Intravenous Iron (Preferred Initial Approach)

Given the severely depleted ferritin (5.62 µg/L), intravenous iron is the optimal first-line treatment 6, 7. IV iron:

• Restores hemoglobin faster than oral iron (mean increase 8 g/L over 8 days) 6
• Bypasses absorption issues
• Avoids gastrointestinal side effects
• More effective when inflammation may be present 6, 2

Dosing options 7:

• Ferric carboxymaltose: 15 mg/kg (max 1000 mg) as single infusion over 15 minutes
• Ferric derisomaltose: Up to 20 mg/kg (max 1500 mg) in 100 mL normal saline
• Iron sucrose: 200-300 mg per dose, multiple doses to reach total of 1000-1500 mg
• Target total dose: 1000-1500 mg to fully replete stores 6, 7

Expected response 6, 7:

• Reticulocytosis at 3-5 days
• Hemoglobin increase of 1-2 g/dL within 4-8 weeks
• Recheck CBC and ferritin at 4-8 weeks post-infusion (not before 4 weeks, as circulating iron interferes with assays) 7

Oral Iron (Alternative if IV Not Accessible)

If IV iron unavailable, use oral iron 5:

• Ferrous sulfate 325 mg (65 mg elemental iron) daily to alternate days 6
• Lower doses (40-60 mg elemental iron) or alternate-day dosing improves tolerance 6
• Take on empty stomach with vitamin C 500 mg to enhance absorption 5
• If not tolerated, take with meals (reduces absorption but improves compliance)
• Avoid calcium, fiber, proton pump inhibitors at same time

Monitor response at 3 weeks: Hemoglobin should increase ≥1 g/dL 1. If no response, switch to IV iron.

Target Goals

• Hemoglobin: Restore to normal range (≥120 g/L for women, ≥130 g/L for men) 6, 8
• Ferritin: Target ≥50 ng/mL in absence of inflammation; ≥100 ng/mL if inflammation present 4, 7, 8
• Transferrin saturation: >20% 4, 8

Common Pitfalls to Avoid

1. Do not assume dietary deficiency alone—always investigate for GI blood loss in adults 1

2. Do not perform repeated phlebotomies—this worsens iron depletion 9

3. Do not check ferritin within 4 weeks of IV iron—results will be falsely elevated 7

4. Do not stop investigation if upper endoscopy is positive—proceed with colonoscopy as dual pathology is common 1

5. Do not use oral iron alone if patient has inflammatory conditions (IBD, chronic disease)—IV iron is superior 6, 4, 2

6. Do not add erythropoietin-stimulating agents—not indicated for simple iron deficiency 6

Follow-Up Monitoring

• Recheck CBC at 4-8 weeks after initiating treatment 7
• Recheck ferritin and transferrin saturation at 4-8 weeks 7
• If recurrent anemia develops, indicates ongoing blood loss or malabsorption—requires re-investigation 8
• Long-term monitoring every 6-12 months once replete, depending on underlying cause 8