Heel prick and CF

Question

My question: Can you see in a heel prick test whether the baby is a carrier of CF? Can parents also be tested at the same time?

Answer

Thank you for this question. We discuss below the general principles of CF screening.
In the first week after birth, every baby in the Netherlands indeed gets a heel prick in order to detect an increased risk of CF. In Belgium, this is not done yet. This large-scale first test is called “screening".
Early detection of CF is important to prevent or limit the health damage. We know that early diagnosis and quick initiation of treatment improves the prognosis for these children.
When a screening test is abnormal, this means that the baby has an increased risk of having the CF disease. This does not mean that the baby has the disease. As you describe the testing is indeed done step by step. A first step is the measurement of the IRT or Immuno Reactive Trypsin. This value will be elevated in infants with CF but may also be temporarily increased in normal babies. If the value is elevated a second test (usually a genetic test) is done on the same sample to detect CF mutations (genetic disorder) or find elevations in PAP a pancreas stress protein that is raised in babies with CF. When the second test is also abnormal, the baby is indeed referred for a sweat test. This sweat test is the ultimate test that will confirm or exclude the diagnosis.

A sweat test is reliable in a baby at a few weeks of age, if he is in good health, and if sufficient sweat can be obtained. Usually, the answer to this test is unambiguous: the sweat chloride is abnormally increased and diagnosis for CF is made or the sweat chloride is perfectly normal and CF is excluded. In some babies, however, the sweat chloride lies between normal and abnormal. In this case, the sweat test is inconclusive and further research is needed. For example, a measurement on rectal tissue can be done.
In a tiny minority of babies it is still, even after several tests, very difficult to give an unequivocal answer. The CF disease can be a very mild and atypical. In the latter case, it is important to follow-up the baby. These infants certainly do not have classical CF, but rather a mild form, or a CF-like disease. The implications of those forms are less than the classic CF disease.

You only have CF if the CF gene for CF on both chromosomes is abnormal. When a newborn is a carrier of CF it means that he has an abnormality on only 1 of the 2 chromosomes. In that case it can be checked if only 1 parent carries an abnormal CF gene (then there is no danger of CF for following children) or whether both parents carry an abnormal CF gene (then there is a chance of CF in other pregnancies).
Based on the given information in your question, we cannot state whether your baby has CF or not or whether your baby is a carrier. We advise you to speak with your doctor, pediatrician or physician involved with the CF screening. We hope this is a sufficient answer to your question.
Best regards,
Prof. K. de Boeck

19.07.2015