Immunoreactive Trypsin

Other names: Trypsin-Like Immunoreactivity; IRT; Serum Trypsinogen

Trypsin is an enzyme, which is used to help the digestion of proteins; trypsin is formed from trypsinogen; trypsinogen is an enzyme, which is produced by the pancreas and converted from an inactive proenzyme to an active enzyme known as trypsin.

Babies with cystic fibrosis may suffer a build-up of trypsin in the blood, as mucus blocks the passageways between the pancreas and the small intestine, meaning that trypsin cannot reach the intestine.

When is the test used?

The test is used primarily to diagnose babies with cystic fibrosis; it is usually ordered when a baby is still very young and the doctor suspects that they have got the condition. The test may be ordered when a baby has symptoms of cystic fibrosis and they do not pass a stool for the first 48 hours of their life.

The IRT test is used as a part of the routine neonatal screening tests in the UK.

How is the test done?

The test is done by collecting and analysing a sample of the patient’s blood; this test is usually carried out on babies and very young children so blood is taken from the heel, rather than the arm. The blood is obtained by using a needle to prick the heel; the blood is then placed on a piece of filter paper and the results are analysed.

What do the test results mean?

If levels of IRT are higher than usual, this may indicate that the baby has cystic fibrosis; it is also possible that the result may be a false positive, so further testing will always be recommended. If the test is negative but the patient has symptoms associated with cystic fibrosis, further testing may be carried out.

The test cannot be used to determine whether people are carriers of cystic fibrosis.

Specific Blood Tests

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