In β-thalassemia major, which hemoglobin type is characteristically elevated on hemoglobin electrophoresis?

Question

Accepted Answer

D. HbF (α~2~γ~2~). ## Hemoglobin Electrophoresis Pattern in β-Thalassemia Major

**Key Point:** β-thalassemia major shows **absent or severely reduced HbA**, **elevated HbF**, and **elevated HbA~2~** on hemoglobin electrophoresis.

### Hemoglobin Composition in β-Thalassemia Major

| Hemoglobin | Normal % | β-Thalassemia Major | Reason |
| --- | --- | --- | --- |
| HbA (α~2~β~2~) | 96–98% | <10% or absent | β-globin chain deficiency |
| HbF (α~2~γ~2~) | <1% | **30–90%** | **Compensatory ↑ γ-globin synthesis** |
| HbA~2~ (α~2~δ~2~) | 2–3% | **4–6%** | Slight ↑ δ-globin synthesis |

**High-Yield:** The **markedly elevated HbF** is the most characteristic finding and distinguishes β-thalassemia major from other hemolytic anemias. HbF does NOT contain β-globin chains, so it is unaffected by β-globin deficiency.

### Mechanism of HbF Elevation

1. Severe β-globin deficiency triggers compensatory γ-globin gene expression
2. γ-globin chains combine with α-globin → HbF production
3. HbF is **protective** against hemolysis (no precipitating α-globin chains in HbF)
4. Patients with higher HbF levels have milder disease (HPFH phenotype)

**Clinical Pearl:** Patients with hereditary persistence of fetal hemoglobin (HPFH) who are homozygous for β-thalassemia mutations remain asymptomatic because they produce sufficient HbF to prevent α-globin precipitation.

**Mnemonic:** **FAD** — **F**etal hemoglobin ↑, **A**bsent HbA, **D**elta (HbA~2~) ↑ in β-thalassemia major.

[cite:Harrison 21e Ch 104]

Answer

A. HbA~2~ (α~2~δ~2~)

Answer

B. HbA (α~2~β~2~)

Answer

C. HbS (α~2~β~2~^S^)

In β-thalassemia major, which hemoglobin type is characteristically elevated on hemoglobin electrophoresis?

Explanation

Hemoglobin Electrophoresis Pattern in β-Thalassemia Major

Hemoglobin Composition in β-Thalassemia Major

Mechanism of HbF Elevation

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Hemoglobin	Normal %	β-Thalassemia Major	Reason
HbA (α₂β₂)	96–98%	<10% or absent	β-globin chain deficiency
HbF (α₂γ₂)	<1%	30–90%	Compensatory ↑ γ-globin synthesis
HbA₂ (α₂δ₂)	2–3%	4–6%	Slight ↑ δ-globin synthesis