How is thalassemia diagnosed in a patient of Mediterranean, African, South‑Asian, or Southeast‑Asian descent who has chronic microcytic, hypochromic anemia unresponsive to iron supplementation and a family history of similar anemia?

Diagnosis of Thalassemia

Order hemoglobin electrophoresis in patients with chronic microcytic hypochromic anemia (MCV <80 fL) that fails to respond to iron supplementation, particularly when the red cell distribution width (RDW) is ≤14% and the patient has Mediterranean, African, South Asian, or Southeast Asian ancestry. 1

Initial Screening Tests

• Measure serum ferritin and transferrin saturation first to exclude iron deficiency before pursuing thalassemia evaluation. Ferritin <30 μg/L confirms iron deficiency, while ferritin >30 μg/L with persistent microcytosis suggests thalassemia trait. 1, 2

• Calculate the RDW from the complete blood count. An RDW ≤14% with microcytosis strongly favors thalassemia minor over iron deficiency, because thalassemic red cells are uniformly small, whereas iron deficiency produces a mixed population of cells yielding RDW >14%. 1

• Examine the red blood cell count. Thalassemia trait typically shows an elevated or high-normal red cell count (often >5 million/μL) despite low MCV, whereas iron deficiency shows a reduced red cell count. 2

• Review the peripheral blood smear for target cells, basophilic stippling, and nucleated red blood cells, which are characteristic morphologic features of thalassemia but absent in uncomplicated iron deficiency. 3

Definitive Diagnostic Testing

• Hemoglobin electrophoresis is the confirmatory test for β-thalassemia, demonstrating elevated hemoglobin A2 (>3.5%) in β-thalassemia minor and elevated hemoglobin F in some cases. 4, 5

• High-performance liquid chromatography (HPLC) provides automated quantification of hemoglobin fractions and has become the standard method for hemoglobinopathy screening in many laboratories. 6

• Molecular genetic testing identifies specific β-globin gene mutations and is particularly useful when electrophoresis results are equivocal, when defining genotypes associated with mild phenotypes, or for prenatal diagnosis. 5, 7

• α-thalassemia requires DNA analysis for diagnosis, because hemoglobin electrophoresis is typically normal in α-thalassemia trait (deletion of 1 or 2 α-globin genes). 3, 7

Diagnostic Algorithm

1. Confirm microcytic anemia is present (MCV <80 fL, hemoglobin below normal for age and sex). 1

2. Obtain iron studies (ferritin, transferrin saturation) and RDW from the complete blood count. 1, 2

3. If ferritin <30 μg/L or transferrin saturation <16%, treat with oral iron for 4 weeks and recheck hemoglobin. 1

4. If ferritin >30 μg/L, RDW ≤14%, and microcytosis persists despite normal iron stores, proceed directly to hemoglobin electrophoresis. 1, 2

5. If hemoglobin electrophoresis shows elevated HbA2 >3.5%, the diagnosis is β-thalassemia trait. 5, 6

6. If hemoglobin electrophoresis is normal but clinical suspicion remains high (appropriate ethnicity, family history, elevated red cell count with microcytosis), order molecular testing for α-thalassemia gene deletions. 3, 7

Common Diagnostic Pitfalls

• Do not assume all microcytic anemia in Mediterranean, African, or Asian patients is thalassemia without measuring iron studies first, because iron deficiency is far more common and these populations are not immune to nutritional deficiency. 1, 4

• Do not order hemoglobin electrophoresis as a first-line test; it is costly and unnecessary when iron studies are abnormal. 1

• Recognize that approximately 50% of thalassemia cases can show elevated RDW, so RDW ≤14% strongly supports thalassemia but RDW >14% does not exclude it. 1

• Avoid misdiagnosing β-thalassemia trait as treatment-resistant iron deficiency anemia. Patients may receive years of unnecessary iron supplementation when the correct diagnosis is thalassemia minor, which requires no treatment. 4

• Do not rely on serum iron alone, as it shows considerable day-to-day variability and overlaps between iron deficiency and thalassemia trait. 1

• Remember that ferritin can be falsely elevated by inflammation, infection, malignancy, or liver disease. In such contexts, add transferrin saturation <20% to confirm true iron deficiency before excluding thalassemia. 1, 2

Family Screening and Genetic Counseling

• Once thalassemia trait is confirmed in a proband, screen first-degree family members (parents, siblings, children) with complete blood count and hemoglobin electrophoresis to identify other carriers. 5, 8

• Provide nondirective genetic counseling to couples in which both partners are carriers, explaining the 25% risk of homozygous β-thalassemia major (transfusion-dependent) or homozygous α-thalassemia (hydrops fetalis) in each pregnancy. 5, 8

• Offer prenatal diagnosis via chorionic villus sampling or amniocentesis with DNA analysis to at-risk couples who wish to know the fetal genotype. 7, 8

• Preimplantation genetic diagnosis is available in specialized centers for couples undergoing in vitro fertilization who wish to select unaffected embryos. 8