Immunoreactive trypsinogen

Measurement of Immunoreactive trypsinogen (IRT) in blood of newborn babies is an assay in rapidly increasing use as a screening test for cystic fibrosis.

IRT is typically raised in cystic fibrosis patients and is measured in routine heel-prick blood taken for biochemical screening of all newborn infants born in the UK. This testing is called the Guthrie Test. Samples with a raised IRT are then screened for common CF gene mutations, and infants with two mutations have a sweat test to confirm the diagnosis. Heterozygous carriers of cystic fibrosis can cause a raised IRT and it is therefore not diagnostic in isolation.