Trypsin-like immunoreactivity; serum trypsinogen, IRT
To screen for cystic fibrosis (CF) in new-born infants
It forms part of the newborn screening programme.
When a newborn infant has signs and symptoms of cystic fibrosis particularly meconium ileus (no stools in the first 24 to 48 hours of life) or where there is a high risk of the baby having the condition
A spot of blood drawn from the infant’s heel and put onto filter paper
Trypsinogen is a proenzyme, an inactive precursor to the proteolytic enzyme trypsin. Normally, trypsinogen is produced in the pancreas and transported to the small intestine. In the small intestine, it is activated, turned into trypsin by an enzyme in the intestinal mucosa, forming a powerful chemical responsible for breaking down the protein in food into smaller pieces called peptides.
It is part of the newborn screening program, and is used to screen for cystic fibrosis.
A blood sample is taken by pricking a newborn's or very young infant's heel and a spot of blood is put onto filter paper.
No test preparation is needed.
Immunoreactive trypsin (IRT) is used to selectively screen for cystic fibrosis (CF) in new-born infants.
This test is used as part of a newborn screen for cystic fibrosis, in cases of meconium ileus (no stools in the first 24 to 48 hours of life), where there are other symptoms and signs suggestive of CF or where a baby is known to be at high risk of having the condition.
IRT testing is not diagnostic; there are a number of false positives and diseases other than CF and pancreatic dysfunction that can cause a positive IRT. An elevated level must be followed with other testing. When diagnosing CF this may include CF gene mutation testing and/or sweat chloride testing.
IRT testing is only useful for screening - it is not diagnostic. There is a substantial rate of false positives due to diseases other than CF and pancreatic dysfunction. An elevated level must be followed with other testing to establish a diagnosis. This may include CF gene mutation testing and/or sweat chloride testing.
If the IRT level is negative but the baby is symptomatic, other testing for CF such as sweat chloride and/or CF gene mutation testing may be considered.
IRT testing will not identify CF carriers. Their trypsinogen production and function will not be affected. In patients who do have CF, the degree of IRT elevation does not reflect the severity of the disease.
Sweat chloride, CF gene mutation
Conditions: Cystic fibrosis, pancreatic cancer, pancreatitis, pancreatic insufficiency, pancreatic diseases
Articles: Screening tests for newborns
Cystic Fibrosis Australia
Better Health Channel: Cystic fibrosis
healthdirect Australia: Cystic fibrosis
Last Review Date: October 10, 2022