Haemoglobinopathy/Thalassaemia screen

Method:

Refer to laboratory, but usually includes Full blood count, Haemoglobin electrophoresis, High performance liquid chromatography (HPLC), Sickle solubility test and Haemoglobin H inclusions.

See Haemoglobin electrophoresis,

Haemoglobin A2,

Haemoglobin F,

Haemoglobin H,

Unstable haemoglobin screening test.

Application:

Investigation of suspected thalassaemia and other haemoglobinopathies, antenatal screening, and screening of partners and families of affected patients. This includes pre-conception testing in at-risk groups, antenatal screening, pre-operative testing in at-risk groups, investigation of unexplained microcytosis and other laboratory findings.

Interpretation:

The hallmark of beta thalassaemia trait is an elevated haemoglobin A2 with a mild microcytic anaemia (in the absence of coexisting iron deficiency).

Iron deficiency can reduce the Hb A2, and therefore lead to a false normal Hb A2 in patients with beta-thalassaemia trait. Outside of pregnancy, analysis should be repeated when the patient is iron replete. In pregnant women, testing should not be delayed whilst treating iron deficiency, as this will delay the identification of at-risk carrier couples.

Alpha thalassaemias are diagnosed by the presence of Hb H bodies (tetramers of beta globin). This test may miss single alpha globin gene deletions (heterozygous a+ thalassaemias, aa/-a, see Thalassaemia).

Haemoglobin S, C, E and the other variants are detected on haemoglobin electrophoresis.

Haemoglobin F is typically significantly elevated in patients with dß-thalassaemia – consult pathologist.

Reference:

Chanarin I. ed. Laboratory Haematology. Churchill Livingstone 1989.

Hartman RC and Jenkins DE. N Eng J Med 1995; 275: 155-157.

Ryan K et al. Significant haemoglobinopathies: guidelines for screening and diagnosis. BJH. 149; 35-49