Neonatal cystic fibrosis screening is a blood test that looks for increased levels of immunoreactive trypsinogen (IRT), an enzyme produced by the pancreas. The test is performed on newborns to diagnose cystic fibrosis (CF).

A sample of blood is either taken from the bottom of the baby's foot of a vein in the arm. A tiny drop of blood is collected onto a piece of filter paper and allowed to dry. The dried blood sample is sent to a lab for analysis.

Your health care provider will explain the test to you, and you must sign a consent form before the test. Some states, but not all, include this test in the newborn screening exams that are done before the mother and baby leave the hospital. 

The brief feeling of discomfort will probably cause your baby to cry.

Infants who have CF may have increased levels of IRT in their blood for several months after birth. A positive IRT test requires follow up testing to confirm the diagnosis.

The predicted value of a normal or negative test is an immunoreactive trypsinogen value less than 140 ng/dL.

Note: ng/dL = nanograms per deciliter

If your child's level of immunoreactive trypsinogen is greater than 140 ng/dL on the first screen, the test result is considered positive. If your child's level is 120 ng/dL on the second screen, the second test result is also considered positive.

Although these two test results indicate CF may exist, a sweat test with a positive result is necessary to confirm the diagnosis.

Risks associated with the test include:

• Infection (a slight risk any time the skin is broken)
• Parental anxiety over false positive tests
• False reassurance over false negative tests

The IRT level does not indicate the severity of the CF. False-positives may occur.