Microcytic Anemia with Elevated RBC Count: Iron Deficiency vs. Thalassemia
This patient has microcytic anemia (low MCH 22.5 pg, low-normal MCHC 30.6 g/dL) with an elevated RBC count (5.46 ×10⁶/µL) and elevated RDW (15.5%), which most likely represents either thalassemia trait or iron deficiency anemia—order a serum ferritin immediately to distinguish between these two conditions.
Interpretation of Laboratory Values
The combination of findings is diagnostically significant:
- Low MCH (22.5 pg): Indicates microcytosis and hypochromia, characteristic of iron deficiency or thalassemia 1
- Elevated RBC count (5.46): When combined with microcytosis, this pattern strongly suggests thalassemia trait, though iron deficiency with secondary polycythemia remains possible 2
- Elevated RDW (15.5%): This is the key discriminating feature—elevated RDW suggests iron deficiency or combined deficiency rather than pure thalassemia, which typically shows normal RDW 1, 3
The elevated RDW is particularly important because it reflects anisocytosis (variation in red cell size), which occurs early in iron deficiency as microcytic cells appear alongside normocytic cells 4. In contrast, thalassemia trait typically produces uniformly small cells with normal RDW 1.
Immediate Diagnostic Workup
Order these tests in the following sequence:
Serum ferritin (most powerful test for iron deficiency):
If ferritin is low (<12-15 μg/dL): Proceed with GI evaluation (see below)
If ferritin is normal/high: Order hemoglobin electrophoresis to confirm thalassemia trait 1
Consider transferrin saturation if ferritin is equivocal (12-100 μg/dL):
- <30% supports iron deficiency 1
Critical Clinical Context Needed
Determine the patient's demographic and clinical profile:
- Sex and menstrual status: If premenopausal woman, menstrual blood loss is the most common cause of iron deficiency 1
- Ethnicity: Mediterranean, Asian, or African ancestry increases thalassemia likelihood 1
- GI symptoms: Any history of blood in stool, melena, dyspepsia, or change in bowel habits
- Medication history: NSAID use is a common cause of occult GI blood loss 1
- Dietary history: Vegetarian diet, poor intake
If Iron Deficiency is Confirmed
For adult men and postmenopausal women with iron deficiency, gastrointestinal blood loss is the primary concern and requires complete evaluation to exclude malignancy 1:
- Upper GI endoscopy with small bowel biopsy (to exclude gastric cancer, celiac disease)
- Colonoscopy or barium enema (to exclude colorectal cancer, polyps, angiodysplasia)
This complete evaluation is mandatory even in the absence of overt bleeding, as asymptomatic gastric and colonic carcinoma commonly present with iron deficiency anemia 1.
For premenopausal women: If menstrual history adequately explains blood loss and ferritin is only mildly low, empiric iron therapy with monitoring may be reasonable before invasive testing. However, maintain a low threshold for GI evaluation if response is inadequate.
Common Pitfalls to Avoid
- Do not assume thalassemia based solely on elevated RBC count—the elevated RDW argues against pure thalassemia and suggests iron deficiency or combined deficiency 1, 3
- Do not skip ferritin testing—it is the most powerful diagnostic test and guides all subsequent management 1
- Do not attribute iron deficiency to diet alone in men or postmenopausal women—GI malignancy must be excluded 1
- Do not rely on MCV alone—combined deficiencies (iron + folate/B12) can normalize MCV while RDW remains elevated 1, 5
Treatment Approach
If iron deficiency is confirmed:
- Initiate oral iron supplementation (therapeutic trial for 3 weeks can confirm diagnosis) 1
- Treat underlying cause identified on GI workup
- Monitor hemoglobin response and repeat ferritin in 3 months
If thalassemia trait is confirmed:
- No iron supplementation needed (unless concurrent iron deficiency documented)
- Genetic counseling if reproductive age
- No further workup required for stable trait