Diagnosis and Management of Microcytic Anemia
Primary Diagnosis
This patient has iron deficiency anemia based on the microcytic indices (MCV 72.1) and elevated RDW (17.2), which is the classic pattern distinguishing iron deficiency from thalassemia trait. 1
The combination of low MCV with RDW >14.0% strongly indicates iron deficiency anemia, while thalassemia minor typically presents with low MCV but RDW ≤14.0%. 1
Diagnostic Confirmation Required
Order serum ferritin immediately as the single most useful diagnostic test, with a cut-off of 45 μg/L providing optimal sensitivity and specificity for iron deficiency. 1, 2
- Ferritin <15 μg/L confirms absent iron stores 1
- Ferritin <30 μg/L indicates low body iron stores 1
- Ferritin >100 μg/dL essentially excludes iron deficiency 2
- If ferritin is between 12-100 μg/dL, add transferrin saturation (<30% supports iron deficiency) since ferritin can be falsely elevated by inflammation, infection, malignancy, or liver disease 2
Critical caveat: Ferritin is an acute phase reactant and can mask concurrent iron deficiency when elevated by inflammatory conditions. 2
First-Line Treatment
Initiate oral ferrous sulfate 200 mg (containing 65 mg elemental iron) three times daily for at least three months after correction of anemia to replenish iron stores. 1, 3
- Alternative formulations include ferrous gluconate or ferrous fumarate if ferrous sulfate causes intolerable gastrointestinal side effects 1
- Adding ascorbic acid enhances iron absorption 1
- A hemoglobin rise ≥10 g/L within 2 weeks confirms iron deficiency diagnosis 1, 2
Mandatory Investigation for Underlying Cause
In a 40-year-old female with confirmed iron deficiency, investigate the source of iron loss—do not assume menstruation alone explains the deficiency. 1
- Evaluate for gastrointestinal blood loss through history of melena, hematochezia, or occult bleeding 1
- Screen for celiac disease if malabsorption is suspected 1
- Consider fast-track GI referral for non-menstruating women with Hb <100 g/L 1
- Investigation should be considered at any level of anemia with confirmed iron deficiency, especially with more severe degrees 1
Alternative Diagnoses to Consider if Iron Studies Are Normal
If ferritin is normal or elevated and transferrin saturation is normal:
- Order hemoglobin electrophoresis if MCV is disproportionately low relative to degree of anemia or patient has appropriate ethnic background for thalassemia 1
- Consider therapeutic trial of pyridoxine (vitamin B6) 50-200 mg daily if sideroblastic anemia is suspected, particularly with family history or unusual presentation 4
- Bone marrow examination may identify ring sideroblasts pathognomonic for sideroblastic anemia if other testing is unrevealing 2, 4
Monitoring Protocol
Check hemoglobin and red cell indices at three-monthly intervals for one year, then after a further year. 1
- Expect hemoglobin increase of at least 2 g/dL within 4 weeks of starting treatment 1
- Provide additional oral iron if hemoglobin or MCV falls below normal 1
- Monitor serum ferritin and transferrin saturation to assess iron store repletion 1
Management of Treatment Failure
If no response to oral iron after 3 weeks:
- Consider intravenous iron if malabsorption is present (expected hemoglobin increase of at least 2 g/dL within 4 weeks) 1
- Evaluate for genetic disorders of iron metabolism (IRIDA, TMPRSS6 defects) or heme synthesis defects (ALAS2, SLC25A38, STEAP3) 1, 4
- For IRIDA, intravenous iron (iron sucrose or iron gluconate) is required as oral iron is typically ineffective 1
Common Pitfalls to Avoid
- Do not assume all microcytic anemia is iron deficiency: Anemia of chronic disease, thalassemia, and sideroblastic anemia must be differentiated to avoid unnecessary iron therapy 1
- Do not overlook combined deficiencies: Iron deficiency can coexist with B12 or folate deficiency 1
- Do not presume ethnicity explains microcytosis: Haemoglobinopathies must be confirmed by laboratory testing, not assumed based on ethnic background alone 2