Cystic fibrosis is caused by mutations in the CFTR gene, which results in thick mucus building up around organs and tissues. This is especially dangerous in the lungs, as it can lead to inflammation, infection, and the formation of scar tissue.
What Is the IRT test?
Immunoreactive trypsinogen (IRT) is an enzyme precursor that is normally made in the pancreas. In cystic fibrosis, IRT can be secreted at higher levels into the bloodstream because of blockages in the pancreatic ducts. IRT tests are part of standard newborn blood screens in the U.S. and the U.K.
IRT levels can also be high following a premature or difficult birth, so a positive test result must be confirmed by additional testing to make a correct cystic fibrosis diagnosis.
How is the IRT test performed?
Within two or three days after birth, a panel of blood tests is carried out, including the IRT test. The test is conducted with a needle to prick the heel of the baby to collect a few drops of blood. The baby may cry from the brief discomfort of the needle, but should not need any treatment following the prick.
What do the test results mean?
If the initial IRT test is positive, a second IRT test at two weeks after birth, or a DNA test is carried out to confirm the results. The choice differs by state in the U.S., but both options allow a diagnosis with a success rate greater than 90 percent.
In cases where two IRT tests are performed and they are both positive for cystic fibrosis, parents in the U.S. will be referred to a Cystic Fibrosis Foundation-approved clinic to confirm the diagnosis, usually with a sweat test and to discuss treatment options.
Two negative IRT test results usually indicate that the baby does not have cystic fibrosis. In cases in which the tests were negative but the baby has some symptoms of cystic fibrosis, further testing will be carried out. A small number of cystic fibrosis cases may not be caught by IRT or other newborn screening tests.