Neonatal cystic fibrosis screeningDefinition: 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
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: 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.
What the risks are: 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
Special considerations: The IRT level does not indicate the severity of the CF. False-positives may occur.
References: Gross SD, Boyle CA, Botkin JR, et al. Newborn Screening for Cystic Fibrosis:Evaluation of Benefits and Risks and Recommendations for State Newborn Screening Programs. MMWR. 2004;53(RR13);1-36. Comeau AM, Parad RB, Dorkin HL, et al. Population-based newborn screening for genetic disorders when multiple mutation DNA testing is incorporated: a cystic fibrosis newborn screening model demonstrating increased sensitivity but more carrier detections. Pediatrics. 2004 Jun;113(6):1573-81.
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