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Diagnosis: Testing: Newborn Screening

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Newborn screening is completed on all infants by collecting blood samples, usually from a heelstick, shortly after birth. These blood samples are collected as blood spots that are allowed to dry on a special filter paper. The dried blood spots are then tested for a variety of diseases. Every state performs newborn screening testing for infants, but not all states include a test for CF.

heel stick

Obtaining blood for newborn screening.

The Maryland newborn screening program began testing for CF in 2006. Most states that test for CF during a newborn screening test for the presence of immunoreactive trypsinogen (IRT) and/or CFTR mutations. IRT is a pancreatic enzyme precursor found in the blood, and the concentration is elevated in babies with CF since pancreatic ducts are partially blocked leading to abnormal enzyme drainage. This occurs even if infants are pancreatic sufficient. If the IRT is elevated in two tests then the infant will be referred for a sweat test.

Some states test only for elevated IRT levels in the blood while other states also test for the presence of CFTR mutations. In these states, if the IRT is high, then the blood will be tested for one or more of the common CFTR mutations. If the baby has two CF mutations, then the infant has CF. If the IRT level is elevated and only one mutation is found, then the newborn screening test is “positive” and the baby may have CF or may be a CFTR mutation “carrier”. Any of these positive newborn screening tests must be confirmed by sweat testing, which remains the “gold standard” for diagnosis of CF.