Trypsin is produced from trypsinogen. Trypsinogen is normally produced in the pancreas and is carried to the small intestine where it changes from an inactive ‘proenzyme’ to the active ‘酵素’胰蛋白酶，用于帮助人体消化蛋白质. ?
在婴儿囊性纤维化，粘液会阻塞从胰脏进入小肠的通道（管道）。粘液会阻止胰蛋白酶原进入肠腔，导致肠壁积聚。酵素 in the blood. This can be detected and measured because ‘immunoreactive’ trypsin (IRT) levels increase in the blood of the infant. Infants with cystic fibrosis at 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 levels fass as the disease of the pancreas (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.