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.