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Infant blood sample

Neonatal cystic fibrosis screening

Definition

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).

Alternative Names

Cystic fibrosis screening - neonatal; Immunoreactive trypsinogen; IRT test

Why the Test is Performed

Children with CF who are diagnosed early in life and start treatment at a young age may have better nutrition, growth, and lung function. Newborn screening tests allow doctors to identify children with CF before they have symptoms.

How the Test is Performed

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.

How to Prepare for the Test

There is no special preparation needed.

Some states include this test in the routine newborn screening tests that are done before the baby leaves the hospital.

If you live in a state that does not perform routine CF screening, your health care provider will explain whether testing is needed.

How the Test Will Feel

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

Risks

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

Considerations

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

Normal Results

Normal values vary from lab to lab. Ask your doctor or testing center for details.

What Abnormal Results Mean

If your child's IRT level is high, further tests will be done to confirm the possibility of CF. Not all children with a positive screening IRT test have CF.

Review Date: 5/1/2007
Reviewed By: Rachel A. Lewis, MD, FAAP, Columbia University Pediatric Faculty Practice, New York, NY. Review provided by VeriMed Healthcare Network.

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