Hb electrophoresis^b

Asymptomatic carrier, mild microcytic anaemia (Hb >10 g/dL)

Compound heterozygous^c: b⁰/b⁺, b⁺/b⁺ (two distinct b⁺ mutations)
Homozygous: b⁰/b⁰, b⁺/b⁺ (two identical mutations)

Severe anaemia, transfusion dependence (Hb <7 g/dL)

Homozygous: b⁺/b⁺
Compound heterozygous^c: b⁺/b⁺, b⁰/b⁺

Intermediate
(Hb 7–10 g/dL)

^a b^wt represents the normal b-globin allele with normal b-globin chain production; b⁺ denotes b-globin mutations that decrease b-globin chain production but do not entirely eliminate it; b⁰ denotes b-globin gene mutations that completely abolish b-globin chain production from the affected allele.
^b Types of haemoglobin (Hb) found on electrophoresis. HbA2, ‘minor’ adult Hb (a₂d₂); HbF, fetal Hb (a₂g₂).
^c Compound heterozygotes are individuals carrying different b⁰ or b⁺ mutations on the two alleles.