What is the diagnostic approach for beta thalassemia?

Diagnostic Approach for Beta Thalassemia

Screen with complete blood count showing MCV <80 fL and MCH <26 pg/dL, then confirm with hemoglobin electrophoresis or HPLC demonstrating elevated HbA2 levels, and use DNA testing for definitive genetic diagnosis when needed.

Initial Screening Tests

Complete Blood Count (CBC) Parameters

• MCV <80 fL is the primary screening threshold that suggests possible beta thalassemia carrier status and warrants further investigation 1
• MCH <26 pg/dL provides 99% sensitivity for detecting beta thalassemia trait 2
• All confirmed beta thalassemia trait cases demonstrate MCV <76 fL, with mean values around 59 fL 2
• The blood picture characteristically shows microcytic hypochromic anemia 2

Screening Indices for Risk Stratification

• Mentzer Index (MCV/RBC count) <12-15 is highly sensitive (97-99%) for distinguishing beta thalassemia trait from iron deficiency anemia 3, 2
• Sehgal index also demonstrates 97.67% sensitivity and can be incorporated as an automated flag in hematology analyzer software 3
• These indices help filter which samples require HPLC testing, improving efficiency 3

Confirmatory Testing

Hemoglobin Analysis

• High-performance liquid chromatography (HPLC) is the definitive confirmatory test for detecting hemoglobin abnormalities and elevated HbA2 levels 4, 5, 3
• Hemoglobin electrophoresis serves as an alternative method for detecting abnormal hemoglobin patterns 4, 5
• Mass spectrometry represents another advanced option for hemoglobin variant detection 5

Iron Studies - Critical Exclusion Step

• Serum iron and total iron-binding capacity must be checked before HPLC in patients with microcytic hypochromic anemia to exclude iron deficiency 3
• Only proceed with HPLC testing in women without iron deficiency, as iron deficiency can mask or confuse the diagnosis 3

Genetic Testing

DNA Analysis for Definitive Diagnosis

• DNA testing for deletions or point mutations in the beta-globin gene provides definitive diagnosis and identifies the specific genetic defect 1, 4
• Massively parallel sequencing (next-generation sequencing) facilitates more precise molecular diagnosis 5
• Genetic testing is particularly important for prenatal diagnosis and family screening 5

Prenatal and Family Screening

Partner Testing Strategy

• When a woman tests positive for beta thalassemia trait, her spouse must be screened to assess risk of having a child with thalassemia major 3
• Cascade testing approach is recommended: test the affected family member first, then perform targeted testing of at-risk relatives 1
• Pre-test genetic counseling should discuss benefits (diagnosis confirmation, reproductive planning) and limitations 1

Prenatal Diagnosis

• Amniocentesis or fetal blood sampling is recommended when both parents are carriers to detect severe forms 1
• Prenatal diagnosis enables prevention of thalassemia births and pregnancy complications 5

Common Diagnostic Pitfalls

• Failure to exclude iron deficiency before proceeding with HPLC leads to misdiagnosis, as both conditions cause microcytic anemia 3
• Missing the diagnosis by not considering ethnicity in the diagnostic approach—beta thalassemia is more prevalent in Mediterranean, Middle Eastern, Southeast Asian, and African populations 1
• Inadequate partner screening—only 55.81% of spouses undergo testing even when indicated, representing a major gap in prevention programs 3
• Relying solely on CBC without confirmatory HPLC or genetic testing, as other conditions can mimic the blood picture 5, 3

Peripheral Blood Smear Findings

• Peripheral smear examination shows microcytic hypochromic red blood cells and should be performed during initial evaluation 4, 3
• This provides supportive evidence but requires confirmation with HPLC or genetic testing 4