This is the sixth part of our series about the condition based on our patient booklet “Fast Facts for Patients: Alpha Thalassemia”. This article focuses on the aspects of screening and diagnosis in alpha thalassemia (AT).
In some parts of the world, all newborn babies have a blood test for thalassemia. A nurse pricks the baby’s heel with a fine needle and squeezes out a drop of blood. This is used to test for other genetic conditions as well.
It is unlikely that the test will find one or two gene changes but it is likely to find HbH AT (three gene changes).
Diagnostic Testing in Children and Adults
A doctor may suggest testing for thalassemia because you (or your child) show some of the symptoms of AT or if a routine blood test shows that you or your child have mild microcytic anemia.
Often, doctors test for iron deficiency first because it’s a common cause of microcytic anemia. They will do other tests to look for HbH AT and AT trait.
These tests can’t show how many AT genes are affected though.
To identify the exact genetic changes, you’ll need to have DNA tests done on a blood sample.
Before having screening tests for thalassemia, you may be offered genetic counseling. This is to make sure you understand any tests you might have and what the results may mean.
Usually, the partners of people with two gene changes on the same chromosome or three gene changes (HbH AT) will also need to have a DNA test.
The counselor will continue to provide support after testing if results show that there is a risk that your children could have three or four gene changes. You will be able to discuss the options when planning a pregnancy.
Some couples decide to have in vitro fertilization (also known as IVF or a ‘test-tube baby’) so that genetic testing can be carried out before the fertilized egg is implanted in the womb. Depending on the gene changes that the parents have, genetic testing can make sure that the baby doesn’t have AT major or doesn’t have any AT gene changes at all.
If you’re already pregnant, your doctor will want to do genetic testing early in the pregnancy in case your baby needs treatment before birth. This helps to prevent premature birth and avoid serious complications for the mother.
If there is a risk that the baby could have AT major, the doctor will suggest testing the baby while still in the womb.
There are different ways to do the test:
- taking a sample of blood from the umbilical cord (cordocentesis)
- testing the fluid surrounding the baby (amniocentesis)
- taking a sample of the placenta (chorionic villus sampling).
Which test you have depends on how far through the pregnancy you are. All the tests carry a small risk of miscarriage, so your doctor will only suggest testing if it is absolutely necessary.
Ultrasound analysis may be used and some non-invasive tests are currently 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.
Invasive sampling means a sample of tissue or fluid is taken from inside the body. This is done via a cut in the skin or through a body opening.
Babies and AT Major
Birth defects are more likely in babies born with AT major, even if they have blood transfusions in the womb. The most common birth defects are minor abnormalities of the genitals in boys. For example, the opening of the urethra (the tube you pee through) can be on the underside of the penis. This is called hypospadias and can be fixed with surgery.
Around 1 in 6 babies (about 17%) have a limb abnormality. These vary in how severe they are. Examples include having hands of different sizes or part of a foot that hasn’t fully developed.
A baby with AT major who does not receive an intrauterine transfusion before he is born will be likely to die in the womb.
Depending on the results of the tests, your counselor may take 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 many factors, including cultural, social, spiritual and religious beliefs.
A pregnant woman with AT needs special care during her pregnancy. Anemia can become more severe. A condition called pre-eclampsia is also more common, which can be fatal if not detected. Signs of pre-eclampsia include rising blood pressure and protein in the urine (signs of damage to the liver or kidneys).
The mother will have regular tests for these during her pregnancy and will often take medication to lower blood pressure.
Please check out the other posts of our series here:
- What Is Alpha Thalassemia?
- Alpha Thalassemia: Genes, Genetic Inheritance and One Gene Change
- Alpha Thalassemia: Two Gene Changes
- Alpha Thalassemia: Three Gene Changes
- Alpha Thalassemia: Four Gene Changes
- Alpha Thalassemia: Symptoms and Treatment
- Alpha Thalassemia: Clinical Trials and New Treatments
- Living with Alpha Thalassemia
Information based on Fast Facts for Patients: Alpha Thalassemia (Karger, 2023).