Immunoreactive Trypsin (IRT) (Whole Blood)

General Information

Please note, this test is part of the New Born Screening Programme and as such is suitable for diagnosis of cystic fibrosis (CF) in the general population. If you suspect that your patient has CF, please call 0121 4240199 to book an appointment for a Sweat Test.

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. 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 can be measured as immunoreactive trypsin (IRT). Infants with cystic fibrosis, 1 to 2 weeks of age show increased levels of IRT 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.