How is thalassaemia diagnosed?
Diagnosis of thalassaemia:
- Haematological indices – reduction in haemoglobin level, size and volume of red blood cell (Mean Corpuscular Haemoglobin – MCH and Mean Corpuscular Volume – MCV)
- A Family Origin Questionnaire: Sickle cell and thalassaemia screening: family origin questionnaire
- Blood film – microcytic and hypochromic red blood cells, anisocytosis, poikilocytosis
- Haemoglobin electrophoresis – detection of different proteins making up haemoglobin molecule – HbA, HbA2, HbF
- Molecular methods – DNA analysis
The screening pathway
We have discussed how thalassaemia is passed on between generations and why we should all be tested.
Let’s turn our attention now to the actual screening process and what is involved.
In England, there is designated NHS Sickle Cell and Thalassaemia genetic screening programme (NHSSCTP) to identify people who are carriers for thalassaemia, sickle cell disease and other haemoglobin disorders. The screening programme targets pregnant women, the biological father and new-born babies. It is important to note that anyone can be screened for thalassaemia at any point of their lives, though carrier status is only detected during infancy from 7 months and above. This test is covered by the NHS.
At the UKTS we believe in informed decision and strongly support being screened for thalassaemia before you think about having children so that you are able to make a decision that is best for you and your family.
How does the screening pathway work for expectant parents?
If already pregnant
- At her first appointment with the midwife, the pregnant woman will be asked to complete a Family Origin Questionnaire (FOQ). The aim of the FOQ is to identify the population groups at highest risk of thalassaemia, sickle cell, and other haemoglobin variants.
- All women – whether they are in high or low prevalence areas – are offered screening for thalassaemia. The actual screening test for thalassaemia, to find out if you are a carrier, is a simple blood test taking just a few minutes. The test should be offered to all pregnant women before they reach 10 weeks and 6 days of pregnancy. It’s really important the test is done early. The result of the blood test is back within a week.
- If the test results show a positive thalassaemia carrier result, the baby’s biological father is offered screening. It is important that the baby’s biological father has a test to see if he is also a carrier as soon as possible.
- Babies can only inherit the condition if both parents are carriers. If tests show the father is not a carrier, the baby will not have a severe form of thalassaemia and the mother will not be offered further tests in pregnancy.
However, it is important to note that there is still a 50% chance that the baby could be a carrier. This is extremely important because when the baby is older, he or she could pass on the unusual gene to his/her children. It is therefore worth trying to find out if the baby is a carrier early on in his or her life. Parents can discuss the implications of their baby being a carrier with their GP or a healthcare professional at their local sickle cell and thalassaemia centre.
What happens if both parents are carriers?
If the blood test reveals the father is also a carrier or the biological father is absent or declines testing, parents will be offered pre-natal diagnosis (PND) in the form of diagnostic tests to determine if their unborn child will have beta thalassaemia. As we have seen, when both parents are carriers, there is a 1 in 4 (25%) chance that the baby could inherit the condition.
A diagnostic test will show if the baby has thalassaemia, is a carrier or if the baby is completely unaffected. Ideally, PND should be performed by 12 weeks and 6 days of pregnancy. The PND method chosen will depend on the gestational age of the foetus (how many weeks of pregnancy have passed) and will be one of the following:
Further counselling and information are provided if the presence of thalassaemia is confirmed, including advice and support for the options of continuation or termination of pregnancy if thalassaemia major is identified.
Counselling and support
These are not easy choices or decisions to make, and it is undoubtedly a very stressful time for the parents.
Some parents decide not to conduct PND for a number of reasons. For example, it may go against their cultural beliefs, or they may not want to take the risk, albeit small, of miscarriage.
Support is available throughout the screening process. If the mother is found to be a carrier of thalassaemia, she will be contacted by a specialist nurse or midwife counsellor for genetic counselling to discuss the result and implications. If the blood tests reveal that both parents are carriers, then they will be offered further counselling to help them through a very difficult time. If the result shows the baby has thalassaemia, the parents will be offered an appointment with a health professional to get information about thalassaemia and talk through their choices.
There is also support available from the charity Antenatal Results and Choices Antenatal Results & Choices
Timing is critical Early access to screening and PND can be critical for couples at increased risk of having a child with thalassaemia. By having the test early, expectant parents can explore and understand all possible options and make informed decisions if their baby is at risk of being born with beta thalassaemia major.
The NHS New-born Blood Spot Screening Programme
The NHS New-born Blood Spot Screening Programme uses the heel prick test – where a few drops of blood are taken from the baby’s heel when it is 5 days old – to test for 9 different health conditions, of which sickle cell disease is one. By identifying any of these conditions early on, treatment can be given promptly. Although thalassaemia is not one of the conditions tested for in the New-born Programme, if a baby has beta thalassaemia major, it will be detected and reported as part of the process. However, the New-born Screening Programme cannot identify carriers of thalassaemia until they are over approximately seven-twelve months in age.
The National Congenital Anomaly and Rare Diseases Registration (NCARDRS) and the National Haemoglobinopathy Registry are usually informed once a diagnosis of thalassaemia is confirmed, unless the person opts out of registration.
Pre-implantation genetic diagnosis allows testing of eggs or embryos from in-vitro fertilisation techniques to allow implantation of disease-free embryos.
Sensitivity is required as prenatal diagnosis, pre-implantation genetic diagnosis, or termination of pregnancy may not be in keeping with the religious or cultural beliefs of the individual/couple. Careful and sensitive handling is also required as the results from any screening tests may sometimes identify possible non-paternity of the baby.