Causes and Treatment of Microcytic Anemia
Iron deficiency anemia is the most common cause of microcytic anemia, accounting for approximately 80% of cases worldwide, followed by anemia of chronic disease, thalassemia, and sideroblastic anemia. 1, 2
Causes of Microcytic Anemia
1. Iron Deficiency Anemia
- Most common cause (80% of microcytic anemia cases)
- Results from:
- Chronic blood loss (gastrointestinal bleeding, menstruation)
- Pregnancy (increased iron requirements)
- Inadequate dietary intake
- Malabsorption (post-bariatric surgery, celiac disease)
2. Anemia of Chronic Disease (ACD)
- Caused by functional iron deficiency due to inflammatory processes
- Underlying conditions include:
- Chronic infections
- Autoimmune disorders
- Malignancies
- Chronic kidney disease
3. Thalassemia
- Inherited disorder of hemoglobin synthesis
- Characterized by very low MCV with normal ferritin levels
- Common in Mediterranean, Middle Eastern, and Southeast Asian populations
4. Sideroblastic Anemia
- Inherited or acquired disorder of heme synthesis
- Characterized by ring sideroblasts in bone marrow
Diagnostic Parameters for Differential Diagnosis
| Parameter | Iron Deficiency | Anemia of Chronic Disease | Thalassemia |
|---|---|---|---|
| MCV | Low (<80 fL) | Low or normal | Very low |
| MCH | Low | Low or normal | Very low |
| Serum Ferritin | Low (<15 μg/L) | Normal or high (>100 μg/L) | Normal |
| TSAT | Low | Low | Normal |
| RDW | Elevated | Normal or slightly elevated | Normal |
Treatment Approaches
1. Iron Deficiency Anemia
- First-line treatment: Ferrous sulfate 200 mg twice daily 1
- Consider adding ascorbic acid (250-500 mg twice daily) to enhance absorption
- Continue therapy for 3 months after anemia correction to replenish stores
- Intravenous iron indicated for:
- Oral iron intolerance
- Non-response to oral therapy
- Malabsorption
- Need for rapid correction
- Options include iron sucrose, ferric carboxymaltose, or iron dextran
2. Anemia of Chronic Disease
- Primary focus: Treat underlying inflammatory condition
- Consider erythropoiesis-stimulating agents (ESAs) if inadequate response to disease management
- Caution: Excessive ESA use increases risk of death, myocardial infarction, stroke, and thromboembolism
3. Thalassemia
- Treatment depends on severity:
- Mild forms may not require specific treatment
- Severe forms may require regular blood transfusions
- Avoid excessive iron supplementation to prevent iron overload
- Iron chelation may be required for transfusion-dependent patients
4. Sideroblastic Anemia
- Treatment directed at underlying cause
- Pyridoxine (vitamin B6) supplementation may help in some cases
Monitoring Response to Treatment
- Check hemoglobin after 2-4 weeks of therapy
- Expect hemoglobin rise by 2 g/dL after 3-4 weeks of iron therapy
- Monitor ferritin and transferrin saturation after 2-4 weeks
- Follow-up CBC at 3-month intervals for one year, then after another year
Special Considerations
Pregnancy
- Higher iron requirements: 30-60 mg/day
- Increase to 60-120 mg/day for anemia
Chronic Kidney Disease
- Target ferritin >100 ng/mL and TSAT >20%
- Consider ESAs with careful monitoring
Post-Bariatric Surgery
- Regular monitoring for multiple nutritional deficiencies
- May require parenteral iron
Clinical Pitfalls to Avoid
- Failing to identify the underlying cause of iron deficiency anemia
- Treating thalassemia with iron supplementation (can lead to iron overload)
- Not continuing iron therapy long enough to replenish stores
- Missing concurrent vitamin deficiencies (B12, folate) that may contribute to anemia
- Overlooking functional iron deficiency in anemia of chronic disease