Cystic Fibrosis (CF) Newborn Screening

Cystic Fibrosis Center

Cystic Fibrosis (CF) Newborn Screening

In the state of Wisconsin, Cystic Fibrosis (CF) is one of 47 disorders for which infants are routinely screened by a heel prick during the first few days of life.

An abnormal cystic fibrosis screening test does not mean a child has cystic fibrosis. It means the child might have cystic fibrosis. An additional test, called a sweat test, is needed to determine whether the child has cystic fibrosis.

The Screening Process

The newborn-screening test for cystic fibrosis involves two steps. First, blood obtained through routine newborn screening is examined for trypsinogen, a substance found to be higher in infants with cystic fibrosis. If the trypsinogen level is elevated, a second test is done on the blood sample to examine it for delta F508, the most common cystic fibrosis gene mutation, and 22 other mutations.

Understanding Newborn Screening for Cystic Fibrosis

There are several ways in which the cystic fibrosis screening test can be abnormal:

  • If the trypsinogen level is extremely elevated but there is no cystic fibrosis gene mutation, there is a small possibility (less than one in 100) that the child has cystic fibrosis. Although the newborn screening test looks for 23 different cystic fibrosis gene mutations, other cystic fibrosis gene mutations exist that are not identified through newborn-screening. A small possibility exists that the child could have two of those other cystic fibrosis gene mutations. Some possible reasons (other than the presence of cystic fibrosis) for elevated trypsinogen levels include a stressful or premature delivery and/or low Apgar scores. If the child has signs of cystic fibrosis or a family history of cystic fibrosis, then the sweat test is needed to be sure the child does not have cystic fibrosis.
  • If the trypsinogen level is elevated and there is one cystic fibrosis gene mutation, there is a one in 20 chance that the child has cystic fibrosis. A single gene mutation is not sufficient for cystic fibrosis, but other cystic fibrosis gene mutations exist. The possibility exists that the child could have a second cystic fibrosis gene mutation not identified through the newborn screening test. A sweat test is needed to determine whether or not the child has cystic fibrosis. Genetic counseling for the parents is also recommended. If a child has one cystic fibrosis gene mutation, then one of the parents is also a carrier of the cystic fibrosis gene mutation. The carrier status of the parents can only be determined by further genetic testing.
  • If the trypsinogen level is elevated and there are two cystic fibrosis gene mutations, the child is presumed to have cystic fibrosis. A sweat test is needed to confirm the diagnosis. Genetic counseling for the parents is also recommended.