IRT is measured in routine heel-prick blood taken for biochemical screening of all newborn infants born in the UK. This test is one of a number of completed in newborn screening (the "Guthrie Test").
The IRT level is identified by taking regular heel-prick blood samples from every newborn baby born in the UK, which serves as part of their overall biochemical screening. This assessment falls under a broader program of newborn screening known as the Guthrie Test.