Immunoreactive Trypsin

At a Glance

Why Get Tested?

To screen for cystic fibrosis (CF) in newborn infants

When To Get Tested?

As part of a newborn screening test

Sample Required?

A blood sample taken from an infant’s heel, a spot of blood that is put onto filter paper

Test Preparation Needed?

None

On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

What is being tested?

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 ‘enzyme’ trypsin which is used to help the body digest proteins.

In babies with cystic fibrosis, mucous can block the passage ways (ducts) from the pancreas into the small intestine. The mucous prevents trypsinogen from reaching the intestines resulting in a build-up of the enzyme 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. 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.

Common Questions

How is it used?

Immunoreactive trypsin (IRT) is used to screen for cystic fibrosis (CF) in new-born infants. In the UK, it is now part of the routine neonatal screening programme.
When is it requested?

This test is used as part of a newborn screen for cystic fibrosis (CF) in all babies in the UK.

IRT testing can not detect all cases of cystic fibrosis (CF) and a positive test can be due to diseases other than CF and other diseases of the pancreas can cause a positive IRT. An elevated level must be followed with other testing. When diagnosing CF this may include: another IRT measurement around 4 weeks later, CF gene mutation testing, and/or sweat chloride testing.
What does the test result mean?

If an IRT level is elevated, a baby may have cystic fibrosis or the elevated IRT may be a false positive result. Elevated levels need to be followed with further testing. If the IRT level is negative but the baby has symptoms, other testing for CF such as sweat chloride and/or CF gene mutation testing may be considered.
Is there anything else I should know?

IRT testing will not identify CF carriers. Their trypsinogen production and function will not be affected. In patients who do have CF, the level of the IRT elevation does not indicate how bad the disease is.
What other tests might my doctor do to check for pancreas function?

Your doctor may request a blood test for amylase, lipase, insulin and c-peptide or HbA1c and faecal elastase to look at other aspects of pancreas and digestive function. IRT can detect pancreatitis at any age but is not routinely used in the UK for this purpose and is not better than amylase or lipase.