Immunoreactive Trypsin
Note: this site is for informational purposes only. To view test results or book a test, use the NHS app in England or contact your GP.
The immunoreactive trypsin test measures the level of immunoreactive trypsinogen in the blood using a heel-prick blood spot sample collected from newborn babies. It is used as part of newborn screening to help identify cystic fibrosis, although further tests are needed to confirm the diagnosis.
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
Common questions
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.
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.
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.
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.
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.