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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 screen for cystic fibrosis (CF). Cystic fibrosis is an inherited disease that causes thick, sticky mucus to build up in the lungs and digestive tract

Alternative Names

Cystic fibrosis screening - neonatal; Immunoreactive trypsinogen; IRT test

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.

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.

Normal Values

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

What abnormal results mean

It is important to remember that a positive screening test for cystic fibrosis does not diagnose cystic fibrosis. If your child's test is positive, further tests will be done to confirm the possibility of CF. Not all children with a positive screening IRT test have CF.

What the risks are

Risks associated with the test include:

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

Special considerations

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

References

Farrell PM, Rosenstein BJ, White TB, et al. Guidelines for diagnosis of cystic fibrosis in newborns through older adults: Cystic fibrosis consensus report. Pediatrics. Aug 2008;153(2).