cf

Question

Dear ladies and gentlemen,

At the heel prick of my son, they discovered a CF gene and in addition an increased value of something. We had to do a sweat test. My son was 3 weeks old at that time. Is this reliable? I read on the internet that it is reliable from 4 to 6 weeks. They also took a biopsy from his rectum. Nothing was found. The conclusion is that he is a carrier. What does this mean for him? Me and my husband are being tested now.

Answer

Thank you for this question. Below, we discuss the general principles of CF newborn screening.

The purpose of the heel prick test is to detect CF at an early stage. We know that early diagnosis and start of treatment, improve the prognosis for these children. This first large-scale test detects babies with an increased risk for CF. We speak in this case of "screening".

When the screening test is abnormal, it means that the baby has an increased risk of having CF. This does not mean that the baby has the disease. As you describe, the testing is indeed done in several steps. The first step is the measurement of IRT or immune reactive trypsin. This value is elevated in infants with CF but may also be temporarily increased in normal babies. When the value is elevated, a genetic test is performed to detect CF mutations (genetic disorder). If 1 or 2 mutations are found, indeed a sweat test will be done. This sweat test is the final test that will confirm or refute the diagnosis of CF.

A sweat test is reliable from the age of a few weeks if the baby is in good health, and if a sufficient amount of sweat can be collected. In most cases the result of the sweat test is clearcut : the sweat chloride is increased and the diagnosis of CF is made or the sweat chloride is perfectly normal and CF is excluded. In some babies, however, the sweat chloride value lies in the intermediate zone: between normal and abnormal. In that case, the sweat test is inconclusive and further tests need to be done. For example, the measurement of ion currents in a rectal biopsy can be used.
In a very small minority of infants it is difficult to give a clear answer, even after several tests. Very mild and atypical types of CF disease do exist. In these cases, it is important to follow the baby further. In these babies, there is certainly no question of a severe kind of CF but it can be a very mild kind of CF or a CF-like disease. The consequences for the child are less severe than for the classic CF disease.

You only have CF if the gene for CF is abnormal on both chromosomes. When a newborn is diagnosed as being a carrier of CF, it means that only one of the two chromosomes is abnormal. In that case we can check whether only 1 parent is a carrier of an abnormal CF gene (then there is no danger for CF in these children) or whether both parents carry an abnormal CF gene (there is a chance of CF in following pregnancies).

Based on the information in your question we cannot provide information about the presence or absence of CF carrier status of your baby. We advise you to speak with your doctors (your pediatrician or physician involved in the CF screening). We hope that this is a sufficient answer to your question. You can read more on the tests mentioned in other questions on this website.

Best regards,
Prof. K de Boeck

22.12.2014