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Children's Hospital of Wisconsin CF Center
(414) 266-6730

University of Wisconsin CF Center
(608) 263-8555

National Cystic Fibrosis Foundation
(800) FIGHT CF

Newborn Screening

What Does an Abnormal CF Screening Test Mean?

In the state of Wisconsin, cystic fibrosis, or CF, is one of twenty-one disorders for which infants are routinely screened by a heel prick during the first few days of life. More information about the State of Wisconsin Newborn Screening program is available at http://www.slh.wisc.edu/newborn/.

An abnormal CF screening test does not mean a child has CF. It means the child might have CF. An additional test, called a sweat test, is needed to determine whether the child has CF.The newborn-screening test for CF involves two steps. First, blood obtained through routine newborn screening is examined for trypsinogen, a substance found to be higher in infants with CF. If the trypsinogen level is elevated, a second test is done on the blood sample to examine it for delta F508, the most common CF gene mutation, and 26 other mutations.

Understanding Newborn Screening for Cystic Fibrosis


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

  1. If the trypsinogen level is extremely elevated but there is no CF gene mutation, there is a small possibility (less than 1 in 100 chance) that the child has CF. Although the newborn screening test looks for 27 different CF gene mutations, other CF gene mutations exist that are not identified through newborn-screening.

    A small possibility exists that the child could have two of those other CF gene mutations. Some possible reasons (other than the presence of CF) for elevated trypsinogen levels include a stressful or premature delivery and/or low Apgar scores.

    If the child has signs of CF or a family history of CF, then the sweat test is needed to be sure the child does not have CF.
  2. If the trypsinogen level is elevated and there is one CF gene mutation, there is a 1 in 20 chance that the child has CF. A single gene mutation is not sufficient for CF, but other CF gene mutations exist. The possibility exists that the child could have a second CF gene mutation not identified through the newborn screening test.

    A sweat test is needed to determine whether or not the child has CF. Genetic counseling for the parents is also recommended.

    If a child has one CF gene mutation, then one of the parents is also a carrier of the CF gene mutation. The carrier status of the parents can only be determined by further genetic testing.
  3. If the trypsinogen level is elevated and there are two CF gene mutations, the child is presumed to have CF.

    A sweat test is needed to confirm the diagnosis. Genetic counseling for the parents is also recommended.