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.

The blood sample is examined for increased levels of immunoreactive trypsinogen (IRT), a protein produced by the pancreas that is linked to CF.

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.

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.

Normal Results

If the test result is negative, the child likely does not have cystic fibrosis. However, if the baby has symptoms of cystic fibrosis, further testing may be needed.

What Abnormal Results Mean

An abnormal (positive) result suggests that your child may have CF. However, 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 result have CF.

Risks

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

Considerations

The test results do not reveal the severity of the CF. False-positives may occur.

Other tests that look for genetic changes known to cause cystic fibrosis may also be used to screen for CF.

Alternative Names

Cystic fibrosis screening - neonatal; Immunoreactive trypsinogen; IRT test

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).

Boat TF, Acton JD. Cystic fibrosis. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 400.

Update Date: 4/1/2012

Reviewed by: Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.