What is being tested?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.
In babies with
cystic fibrosis, mucous plugs can block the pancreatic ducts that lead into the small intestines, preventing trypsinogen from reaching the intestines resulting in a buildup of the protein in the blood. This iscan be measured as immunoreactive trypsin (IRT). Infants with cystic fibrosis 1 to 2 weeks of age show increased levels of IRT in the plasma in the neonatal heal-prick test. It is currently the best screening test for cystic fibrosis but cannot be done after the first few weeks of life since it falls as pancreatic insufficiency develops. Several factors other than cystic fibrosis can affect the test result and therefore not all babies with high IRT will have cystic fibrosis. Where an elevated level is obtained, further investigation either by sweat testing or genetic analyses may be required.
