Hematology Oncology · Year 2 · from Hematology Oncology
Case 3: Beta-Thalassemia Trait Misdiagnosed as Iron Deficiency
Patient Presentation
Demographics: 32-year-old female of Greek ancestry
Chief Complaint: Referred for persistent microcytic anemia despite iron supplementation
History of Present Illness: The patient was found to have microcytic anemia during routine prenatal labs for her first pregnancy. Her primary care physician prescribed ferrous sulfate 325 mg three times daily for presumed iron deficiency. After 3 months of treatment, her MCV remains low and she was referred to hematology. She denies fatigue, bleeding, or GI symptoms. Her mother and sister were told they have "mild anemia."
Physical Examination:
- Vital signs: Normal
- General: Well-appearing woman, not pale
- HEENT: No pallor, no jaundice
- Cardiac: Regular rate, no murmurs
- Abdomen: Gravid uterus, no hepatosplenomegaly
- Extremities: No edema
Workup and Results
Complete Blood Count:
- WBC: 7,200/uL
- Hemoglobin: 10.8 g/dL (mildly low)
- MCV: 64 fL (markedly low)
- MCH: 22 pg
- RBC count: 5.8 million/uL (elevated)
- RDW: 14% (normal)
Iron Studies:
- Serum iron: 95 mcg/dL (normal)
- TIBC: 320 mcg/dL (normal)
- Ferritin: 180 ng/mL (normal, likely elevated from iron supplementation)
- Transferrin saturation: 30% (normal)
Hemoglobin Electrophoresis:
- HbA: 94.5%
- HbA2: 5.8% (elevated, normal < 3.5%)
- HbF: 0.7%
Calculations:
- Mentzer index (MCV/RBC): 64/5.8 = 11 (< 13 suggests thalassemia)
Diagnosis
Beta-Thalassemia Trait (Beta-Thalassemia Minor)
Distinguishing from iron deficiency:
| Feature | Iron Deficiency | Thalassemia Trait |
|---|---|---|
| Ferritin | Low | Normal/High |
| TIBC | High | Normal |
| RBC count | Low/Normal | High |
| RDW | High | Normal |
| HbA2 | Normal | Elevated (> 3.5%) |
| Mentzer index | > 13 | < 13 |
Treatment Plan
- Stop iron supplementation:
- No iron deficiency present
- Continued iron may cause iron overload
- Prenatal counseling:
- Test father for thalassemia trait
- If both parents are carriers: 25% risk of thalassemia major in offspring
- Offer genetic counseling and prenatal diagnosis
- No treatment needed for thalassemia trait:
- Mild anemia does not require treatment
- Patient should understand this is inherited, not nutritional
- Provide documentation to prevent future inappropriate iron therapy
- Family screening:
- Offer testing to siblings and other family members
- Important for reproductive counseling
Teaching Points
- Thalassemia trait causes microcytosis disproportionate to the degree of anemia
- The RBC count is elevated (producing more small cells to compensate)
- RDW is normal (uniform population of small cells) vs. elevated in iron deficiency
- HbA2 > 3.5% is diagnostic of beta-thalassemia trait
- The Mentzer index (MCV/RBC) < 13 suggests thalassemia; > 13 suggests iron deficiency
- Iron supplementation is not indicated and may be harmful
- Genetic counseling is essential for reproductive decision-making