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PTD - 250 

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

Usually performed as part of neonatal screening at birth by Paediatrics.

Request Form

Combined Pathology Blood form (Yellow/Black)


Analysed by Protein Reference Unit, Sheffield 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.

Patient Preparation

None required.

Turnaround Time

2 weeks


Blood spot collected onto a Guthrie card. Ensure complete permeation and drying of blood spot before transport.

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

Causes for Rejection

Specific criteria not met.

Reference Range

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

Lab. Handling

Processing: Store guthrie card at 4C in the separating fridge (CB39).
Referral: SASOD and send.

Version 1.0 / July  2014                                                                                                           Approved by: Consultant Biochemist