Also Known As
Trypsin-like immunoreactivity
Serum trypsinogen
Formal Name
Immunoreactive trypsin (IRT)
This article was last reviewed on
This article waslast modified on 10 October 2023.
At a Glance
Why Get Tested?

To screen for cystic fibrosis (CF) in newborn infants

When To Get Tested?
Sample Required?

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

Test Preparation Needed?


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.

Accordion Title
Common Questions