Patient Test Information

Immunoreactive Trypsinogen

Also known as:

Trypsin-like Immunoreactivity; Immunoreactive Trypsin; Serum Trypsinogen; IRT

Formal name:

Immunoreactive Trypsinogen

Related tests:

Chymotrypsin; Sweat Test; CF Gene Mutation Testing

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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 drawn from an infant's heel, a spot of blood that is put onto filter paper, or a blood sample drawn from a vein in your arm

Test Preparation Needed?

None

How is it 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 mid-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)

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. An elevated level must be followed 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.

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.

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 that lead into the small intestine, preventing trypsinogen from reaching the intestine and preventing the breakdown of food proteins.

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.

Damage to the pancreas caused by other diseases, such as chronic pancreatitis and pancreatic cancer, may 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.

How is the sample collected for testing?

A blood sample is drawn from a newborn's or very young infant's heel, a spot of blood is put onto filter paper, or a blood sample is drawn from a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

  1. 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.

  2. Will every newborn be tested for CF?

    Yes. Cystic fibrosis screening is now a required part of newborn screening in all 50 states in the U.S. The IRT test is one of the tests that may be used for screening.

  3. How is CF treated?

    Currently, there is no cure for cystic fibrosis, only treatments aimed at minimizing the severity of the symptoms and improving quality of life. Read the article on Cystic Fibrosis, Treatment to learn more.