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Alpha thalassaemia screen

Test category:

Familial - Haematological; Reproductive - Carrier screen

Use of test

Purpose:

There are two alpha globin genes (HBA1 and HBA2) which produce proteins which contribute to haemoglobin. Patients normally have four copies of the HBA gene, two from each parent. Mutations in these genes can cause alpha thalassaemia (of varying severity) or result in no clinical abnormality (being an unaffected carrier for thalassaemia). Deletions affecting the HBA genes are the most common cause of alpha thalassaemia, although rare non-deletional mutations may also cause the disease. Patients can also have extra copies of the HBA gene, which may have clinical implications.

This test detects deletions of the HBA  genes which contribute to >90% of alpha thalassaemia diagnoses. The test also detects extra copies of the HBA genes and the most common non-deletional HBA gene mutation, which causes Hb Constant Spring. The result can have diagnostic and familial implications.

Utility:

A normal test result indicates that the patient is unlikely to be a carrier for thalassaemia but does not exclude the possibility.

The presence of deletions that affect 1 - 2 copies of the HBA genes are unlikely to have significant clinical features of thalassaemia and indicates that the patient is a carrier for alpha thalassaemia.

The presence of deletions that affect 3 - 4 copies of the HBA genes are associated with clinical features of alpha thalassaemia.

Extra copies of the HBA genes are only relevant if the patient also inherits beta thalassaemia, as more severe clinical features of this disease may result.

The presence of the Constant Spring mutation on its own indicates the patient is a carrier for alpha thalassaemia. The presence of deletions affecting 2 - 3 copies of the HBA genes along with the Constant Springs mutation is associated with clinical features of alpha thalassaemia.

Ethical considerations:

This is an assay for heritable mutations. It may raise issues of ethics or consent that are different from most other investigations ordered in the routine care of a patient. Use of the Sonic Genetics consent form (below) is not mandated, but could be used to guide the discussion with the patient.

In the case of carrier testing of an unaffected child, national regulations require that the laboratory has evidence of pre-test counselling by a genetics professional and written consent.

Consent form:

Download the Sonic Genetics consent form.

Methodology:

Multiplex Ligation Probe Amplification (MLPA) analysis of the HBA1 and HBA2 genes.

Requesting the test

Ordering:

This test can be requested by any medical practitioner. Please include details of relevant investigations (see below).

Sample required: 

4 mL blood in EDTA (separate tube required). Specimens may be collected by the requesting practitioner or at any Sonic Healthcare collection centre (see link below).

To help ensure the quality of the test, a genetic test should be done with a dedicated sample whenever possible i.e. a sample collected specifically for that test rather than a sample that is used for multiple tests.

We recommend that the patient or another adult check the labelling of request forms and sample tubes.

>Link to Sonic Healthcare collection centres

Special instructions:

This test should be preceded by a review of red blood cell indices and morphology (FBC, MCV, MCH, HbH inclusions), exclusion of Fe deficiency anaemia (Fe studies, ferritin) and investigation for abnormal haemoglobins (Hb-electrophoresis, HbF and HBA2 levels).

Turnaround time:

15 business days.

Price:

$250.

Rebate:

This test is not rebated by Medicare. The laboratory assumes that the patient or client has provided informed financial consent for the test.

Click here for our billing policy.