Neonatal cystic fibrosis screening is a blood test that screens newborns for cystic fibrosis (CF).
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 or 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). This is 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
Cystic fibrosis is a disease passed down through families. CF causes thick, sticky mucus to build up in the lungs and digestive tract. It can lead to breathing and digestive problems.
Children with CF who are diagnosed early in life and start treatment at a young age may have better nutrition, growth, and lung function. This screening test helps doctors 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.
Other tests that look for genetic changes known to cause cystic fibrosis may also be used to screen for CF.
If the test result is negative, the child likely does not have cystic fibrosis. If the test result is negative but the baby has symptoms of cystic fibrosis, further testing will likely be done.
What Abnormal Results Mean
An abnormal (positive) result suggests that your child may have CF. But it is important to remember that a positive screening test does not diagnose cystic fibrosis. If your child's test is positive, more tests will be done to confirm the possibility of CF.
Not all children with a positive result have CF.
Risks associated with the test include:
Infection (a slight risk any time the skin is broken)
Anxiety over false positive results
False reassurance over false negative results
Farrell PM, Rosenstein BJ, White TB, et al. Guidelines for diagnosis of cystic fibrosis in newborns through older adults: Cystic fibrosis consensus report. Pediatrics. 2008;153:S4-S14.
Boat TF, Acton JD. Cystic fibrosis. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 395.
Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.