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
Request on ICE
Analysed by referral laboratory if specific criteria met.
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.
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
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
The upper 98th centile level in blood is 70 ug/L.
Falsely high results are found in renal failure, acute
pancreatitis and obstruction