Pathology Handbook

Immuno-reactive Trypsin



Clinical Indications

Immuno-reactive trypsin (IRT) levels may be used to screen for cystic fibrosis (CF) in neonates, raised levels suggesting CF.

The test is most sensitive up to the age of 6 weeks and will NOT be carried out on older children.

In children older than 2 months a sweat test is probably more appropriate.

Request Form

Request on ICE


Analysed by referral laboratory if specific criteria met.

Specific Criteria

The test is offered on babies with specific symptoms of CF, and also on siblings of confirmed CF children. The baby should be on oral feeds at the time of collection. Full details should be sent with the request.

Turnaround Time

2 weeks


Blood spot collected onto a Guthrie card.  Ensure complete permeation and drying of blood spot before transport. It is recommended to collect 2 samples, 3 days apart.


The blood spot should have completely permeated the card and dried before placing in a plastic bag and transporting to the laboratory.

Lab Handling

Sent to referral laboratory (Addenbrooke's Hospital)

Causes for Rejection

Unlabelled or incorrectly labelled sample; not meeting specific criteria for analysis; if child is >6 weeks of age

Reference Range

The upper 98th centile level in blood is 70 ug/L.

Falsely high results are found in renal failure, acute pancreatitis and obstruction