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Patient Test Information

Immunoreactive Trypsinogen (IRT)

  • Why Get Tested?

    To screen for cystic fibrosis (CF); sometimes to detect pancreatitis

    When To Get Tested?

    As part of a newborn screening test; sometimes when you have symptoms of pancreatitis, such as severe abdominal pain that may be persistent or intermittent, nausea, vomiting, weakness, and jaundice

    Sample Required?

    A blood sample collected by pricking the heel of the infant and collecting a few drops of blood in a small tube or as a spot of blood on filter paper; a blood sample drawn from a vein

    Test Preparation Needed?

    None

  • What is being tested?

    Trypsinogen is an inactive precursor produced by the pancreas that is converted to the enzyme trypsin. This test measures the amount of trypsinogen in the blood.

    Normally, trypsinogen is produced in the pancreas and transported to the small intestine. In the small intestine, it is activated and converted to trypsin. Trypsin is one of the enzymes responsible for breaking down the protein in food into smaller pieces called peptides. Without sufficient trypsinogen and trypsin, a person will not be able to properly digest and use proteins. Any condition that prevents trypsinogen from reaching the small intestine may cause an increase in trypsinogen in the blood. 

    In people with cystic fibrosis (CF), mucus plugs can block the pancreatic ducts, preventing trypsinogen from reaching the small intestine, resulting in decreased breakdown of food proteins.

    Damage to the pancreas caused by other diseases, such as chronic pancreatitis and pancreatic cancer, may also cause blockages that prevent trypsinogen from reaching the small intestine. The cells that produce trypsinogen can also become damaged or be destroyed, decreasing the body's supply.

    As part of a group of newborn screening tests, infants may be screened for CF using a test called immunoreactive trypsinogen (IRT). Newborns with CF may have elevated levels of IRT.

  • How is the test used?

    Immunoreactive trypsinogen (IRT) is used as part of some newborn screening programs to screen for cystic fibrosis (CF). It may be used in conjunction with a sweat chloride test and/or a cystic fibrosis gene mutation panel to help identify CF.

    IRT may also sometimes be used to help detect acute pancreatitis.

    When is it ordered?

    This test may be ordered soon after a baby is born as part of a newborn screen for cystic fibrosis. Cystic fibrosis screening is now a required part of newborn screening in all 50 states in the U.S. Immunoreactive trypsinogen (IRT) is one of the tests used by some states to screen for CF.

    An IRT test sometimes is ordered when a person has signs and symptoms of acute pancreatitis, such as:

    • Severe pain in the upper abdomen that may radiate to the mid-back, which usually lasts at least several hours at a time
    • Nausea, vomiting
    • Weakness
    • Yellowing of the skin and/or eyes (jaundice)
    • Fever

    What does the test result mean?

    If an IRT level is elevated, a newborn may have cystic fibrosis (CF).

    If the IRT is elevated, a child or adult may have abnormal pancreatic enzyme production, pancreatitis, or pancreatic cancer.

    However, IRT testing is not diagnostic. There are a fair number of false positives and problems other than cystic fibrosis and pancreatitis that can cause an elevated IRT. Factors such as age at collection and race/ethnicity could affect IRT levels. An elevated level must be followed up with other testing. When diagnosing cystic fibrosis, this may include another IRT test in a month, CF gene mutation testing, and/or sweat chloride testing.

    If the IRT level is not elevated, then it is likely that the newborn does not have CF. However, if suspicion of CF is high and the infant has signs and symptoms consistent with CF, other testing for cystic fibrosis, such as sweat chloride and/or CF gene mutation testing, should be considered.

    What other tests might my healthcare practitioner do to check pancreas function?

    Your healthcare practitioner may order a stool test for fecal fat, fecal elastase, or chymotrypsin or a blood test for amylase or lipase to look at other aspects of pancreas and digestive function.

    Is there anything else I should know?

    In testing for cystic fibrosis (CF), the IRT test is only useful for screening. Additional testing is needed to establish a diagnosis.

    In those who do have CF, the degree of IRT elevation does not reflect the severity of the disease.

  • View Sources

    Sources Used in Current Review

    2020 review performed by Jayson V. Pagaduan, PhD, Clinical Chemist, Intermountain Healthcare.

    Therrell, B.L., Jr., et al. Immunoreactive Trypsinogen (IRT) as a Biomarker for Cystic Fibrosis: challenges in newborn dried blood spot screening. Mol Genet Metab, 2012. 106(1): p. 1-6.

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    Weidler, S., et al. A product of immunoreactive trypsinogen and pancreatitis-associated protein as second-tier strategy in cystic fibrosis newborn screening. J Cyst Fibros, 2016. 15(6): p. 752-758.

    Castellani, C. and J. Massie. Emerging issues in cystic fibrosis newborn screening. Curr Opin Pulm Med, 2010. 16(6): p. 584-90.

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