First Step in Evaluating Iron Deficiency Anemia
The first step to evaluate iron deficiency anemia is to confirm the diagnosis with laboratory testing, specifically hemoglobin level and serum ferritin. 1, 2
Diagnostic Criteria for Iron Deficiency Anemia
Iron deficiency anemia is defined by:
- Hemoglobin < 13 g/dL in men or < 12 g/dL in non-pregnant women, AND
- Ferritin < 45 ng/mL 1
Key Laboratory Tests
Complete Blood Count (CBC) with indices
- Hemoglobin level
- Red cell indices (MCV, MCH, MCHC)
- Peripheral blood smear evaluation
Iron Studies
- Serum ferritin (most powerful test for iron deficiency) 1
- Serum iron
- Total iron-binding capacity (TIBC)
- Transferrin saturation
Interpretation of Laboratory Results
| Parameter | Iron Deficiency Anemia | Anemia of Chronic Disease |
|---|---|---|
| MCV | Low (microcytic) | Normal |
| Serum iron | Low | Low |
| TIBC | High | Low/Normal |
| Ferritin | < 30 μg/L | > 100 μg/L |
| Transferrin saturation | < 15% | < 20% |
Important Considerations
- Ferritin interpretation: Since ferritin is an acute phase reactant, levels should be interpreted in the context of patient-specific conditions, such as chronic kidney disease and underlying inflammatory states 1
- Sensitivity of CBC alone: Relying solely on hemoglobin and hematocrit without measuring iron status indicators may miss iron depletion that could quickly progress to deficiency 3
- Reticulocyte count: Helps assess bone marrow response to anemia; low reticulocyte index indicates decreased production 2
Next Steps After Diagnosis
After confirming iron deficiency anemia, the evaluation should proceed based on patient demographics:
All postmenopausal women and all men: Upper and lower GI investigations should be considered unless there is a history of significant overt non-GI blood loss 1
All patients: Should be screened for celiac disease 1
Premenopausal women: Screening for celiac disease is recommended, but other GI investigations should be based on clinical judgment 1
Common Pitfalls to Avoid
Relying solely on hemoglobin/hematocrit: These decrease only when severe iron depletion is present and can be misleading 3
Failing to interpret ferritin in context: In inflammatory states, ferritin may be falsely elevated despite iron deficiency 1, 2
Missing underlying causes: GI blood loss from colonic or gastric cancer and malabsorption in celiac disease are important causes that need to be identified 1
Delaying investigation: The lower the hemoglobin, the more likely there is serious underlying pathology and the more urgent the need for investigation 1
By following this systematic approach to diagnosis, clinicians can accurately identify iron deficiency anemia and proceed with appropriate investigations to determine the underlying cause, ultimately improving patient outcomes.