Microcytic Hypochromic Anemia: Iron Deficiency Anemia
This patient has iron deficiency anemia (IDA) and requires immediate oral iron supplementation with ferrous sulfate 200 mg three times daily, along with investigation for the source of iron loss. 1
Diagnostic Interpretation
The laboratory values definitively indicate iron deficiency anemia:
- Hemoglobin 9.7 g/dL represents moderate anemia requiring treatment 2
- MCV 75 fL confirms microcytosis (normal 80-100 fL), with microcytic anemia <80 fL most commonly caused by iron deficiency 2
- MCH 20 pg and MCHC 19.5 g/dL are both markedly reduced, indicating hypochromia characteristic of iron deficiency 1, 3
- The combination of low MCV with low MCH and MCHC strongly distinguishes IDA from thalassemia trait, which typically shows disproportionately low MCV relative to hemoglobin with normal or near-normal MCHC 1, 4
Essential Confirmatory Testing
Order these tests immediately to confirm diagnosis and guide treatment:
- Serum ferritin is the single most powerful diagnostic test: <15 μg/L is diagnostic (specificity 0.99), <30 μg/L indicates depleted iron stores, and <45 μg/L warrants investigation 1
- Iron studies including serum iron, total iron-binding capacity (TIBC), and transferrin saturation: expect low iron, high TIBC, and transferrin saturation <15% in IDA 2
- RDW (red cell distribution width): elevated RDW (>14%) strongly supports IDA over thalassemia trait, which typically shows normal or low RDW 1, 5
- Reticulocyte count to assess bone marrow response and rule out hemolysis 2
Immediate Treatment Protocol
Start oral iron replacement without waiting for confirmatory tests given the clear clinical picture: 1
- Ferrous sulfate 200 mg (65 mg elemental iron) three times daily is first-line therapy 1, 6
- Do not crush or chew tablets 6
- Adding ascorbic acid (vitamin C) enhances iron absorption 1
- Alternative formulations (ferrous gluconate, ferrous fumarate) if ferrous sulfate not tolerated 1
- Continue for at least 3 months after anemia correction to replenish iron stores 1
Expected response: Hemoglobin should rise ≥10 g/L (≥1 g/dL) within 2 weeks if iron deficiency is the cause 7
Investigation for Source of Blood Loss
Do not assume dietary deficiency explains the anemia—full investigation is required: 1
- Upper GI endoscopy should be performed first, revealing a cause in 30-50% of patients 1
- Obtain small bowel biopsies during endoscopy to screen for celiac disease (present in 2-3% of IDA patients) 1
- Colonoscopy should follow, particularly prioritized in patients over 50 where colonic pathology is more likely 1
- In premenopausal women, assess menstrual blood loss as a potential source 8
- Consider malabsorption disorders, dietary inadequacy, and medications 2
Monitoring Strategy
- Follow hemoglobin and red cell indices at 3-monthly intervals for one year, then after a further year 1
- Provide additional oral iron if Hb or MCV falls below normal 1
- If no response after 2 weeks of adequate oral iron therapy, consider parenteral iron dextran for malabsorption, losses exceeding maximal oral replacement, or true intolerance 8
Critical Pitfalls to Avoid
- Do not overlook combined deficiencies: If RDW is markedly elevated, this may indicate coexisting folate or B12 deficiency masking the full picture—check vitamin B12 and folate levels 1, 7
- Do not miss thalassemia trait: If MCV is disproportionately low relative to degree of anemia (MCV <70 with Hb >10), RBC count is elevated, or iron studies return normal, order hemoglobin electrophoresis 1, 5
- Do not assume normal ferritin excludes iron deficiency in inflammatory states: Ferritin up to 45-100 μg/L may still represent iron deficiency with concurrent inflammation 9, 1
- Do not rely on MCV alone: The low MCHC (19.5 g/dL) is particularly specific for iron deficiency and helps distinguish it from thalassemia trait 4, 3