Some states offer a newborn test for cystic fibrosis. The test, called the assay for immunoreactive trypsinogen (IRT), measures levels of the IRT digestive enzyme. Abnormally high levels of IRT suggest cystic fibrosis. Some states also test for common gene mutations that indicate cystic fibrosis.

Experts continue to debate how helpful newborn screening is for children who do not have any symptoms of cystic fibrosis. No studies in the United States show a reduction of lung disease in cystic fibrosis patients detected by newborn screening.^{1, 2} But newborn screening for this disease does improve children's nutrition and growth.² The Centers for Disease Control and Prevention (CDC) believes state newborn screening is worthwhile. The benefits to patients depend on how well the tests are carried out and followed up.