Neonatal cystic fibrosis screening

Alternative names
Cystic fibrosis screening - neonatal; Immunoreactive trypsinogen

Definition

Neonatal cystic fibrosis screening is a pancreatic test that evaluates immunoreactive trypsinogen. The test is performed on newborns to determine whether the baby has cystic fibrosis (CF).

How the test is performed

A small amount of blood is drawn from the newborn after the area is cleansed with antiseptic. The blood is collected onto a test strip.

How to prepare for the test

Your health care provider will explain the test to you, and that false-positive and false-negative results are possible. You must sign a consent form before the test. Some states are moving toward including this in the battery of newborn screening tests that are done on all neonates prior to hospital discharge. Ask your health care provider if this is true in your state.

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 genetic disease that affects the sweat glands as well as the respiratory and gastrointestinal systems. Trypsinogen is produced by the pancreas, and babies with cystic fibrosis have elevated levels. This is a screening tool to identify infants who need further testing to confirm the diagnosis.

Normal Values

The predicted value of a normal or negative test is an immunoreactive trypsinogen value less than 140 ng/dL.

Note: ng/dL = nanograms per deciliter

What abnormal results mean

Abnormal results, and the strength of the test in predicting CF, is based on where your child’s test results fall in relation to the values of all tested children to date and whether the test is positive on repeat examination.

If your child’s level of immunoreactive trypsinogen is greater than 140 ng/dL on the first screen, the test result is considered positive. If your child’s level is 120 ng/dL on the second screen, the second test result is also considered positive.

Although these two test results indicate CF may exist, a sweat test with a positive result confirms the diagnosis.

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

Johns Hopkins patient information

Last revised: December 4, 2012
by Amalia K. Gagarina, M.S., R.D.

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