This is the third part of our series about the condition based on our patient booklet “Fast Facts for Patients: Beta Thalassemia”. This article focuses on the screening for and diagnosis of beta thalassemia (BT).
In some parts of the world all newborn babies are screened for several genetic conditions. A nurse will prick the baby’s heel with a fine needle and squeeze out a drop of blood, which is then used for the testing. The heel prick test is not a reliable test for all types of thalassemia but it can pick up BT major.
Children with the most severe forms of BT can develop symptoms from 3 months of age.
If your child has symptoms that suggest they may have BT, your doctor will request blood tests. These tests look for iron deficiency to rule out the commonest cause of anemia.
The blood tests will also analyze the Hb level, the shape and size of the red blood cells and look for changes in the structure of the Hb molecule. Carriers of a BT gene change and people with BT have red blood cells that are smaller than normal. This is a particular feature of BT called microcytosis. The specific test for BT is usually HPLC – high performance liquid chromatography – or sometimes electrophoresis.
Microcytosis is the term used to describe red blood cells that are unusually small.
More than 400 gene changes are associated with BT. DNA (genetic) tests need to be done on a blood sample to identify the specific ones you have. The sample may need to be sent to a specialized laboratory for these tests.
Depending on your ethnic background or family history, your doctor may suggest you have blood tests for thalassemia if you are planning to start a family.
Ideally, tests for BT should be carried out before the start of pregnancy. But in practice, most women usually have blood tests when they first go to their doctor after becoming pregnant. If your blood test shows anemia and/or small red blood cells, your doctor is likely to suggest further testing for BT. If you are found to have BT trait (one changed gene), the baby’s father will also need to be tested, to see if there is a risk your baby could be born with BT.
Genetic Counseling and Pregnancy
If your doctor suspects you have a BT gene change, they may suggest genetic counseling for you and your partner. The counselor will help you understand why you are considered a ‘couple at risk’ for BT and will explain what your test results mean.
If the blood test results show there is a risk that your child could be born with BT, the counselor will continue to provide support. You will also be able to discuss your options when planning a pregnancy. Some couples opt to have in vitro fertilization (IVF or a test tube baby) so that genetic testing can be carried out before the fertilized egg is implanted. This makes sure that the baby doesn’t have BT.
If you are already pregnant and there is a risk that the baby has BT, it’s possible for the baby to be tested while still in the womb. This is usually done in one of two ways:
- taking a small sample of the placenta (chorionic villus sampling)
- testing the fluid surrounding the baby (amniocentesis).
Which test you have depends on how far through the pregnancy you are. Both tests carry a small risk of miscarriage, so your doctor will only suggest testing if absolutely necessary.
There are some non-invasive tests that are under investigation, such as testing fetal DNA found in the mother’s bloodstream. These may be useful in future, but they are currently not accurate enough to use for thalassemia and give high levels of wrong results.
If tests suggest that a baby may be born with severe BT, your counselor may guide you through the difficult decision of whether to continue with the pregnancy. There is no single answer that suits every couple. The decision depends on lots of different factors, including cultural, social, spiritual and religious beliefs. Being fully informed about the disease will help you make a decision.
Information based on Fast Facts for Patients: Beta Thalassemia (Karger, 2023).