Serum-immunoreactive-trypsin concentrations in cystic fibrosis [letter].

We measured immunoreactive trypsin (IRT) concentrations in 32 patients with established cystic 
fibrosis and in 16 parents (heterozygotes) of patients with CF. 29 
patients (91%) and 6 parents (38%) had abnormal trypsin concentrations. We 
found that in only 3 out of the 29 patients with 
abnormal IRT was the concentration supranormal. Our data suggest that low 
IRT concentrations are an excellent index of diminished pancreatic reserve in 
CF and that serum-IRT concentration would be a useful diagnostic test. 
The fact that CF patients at birth invariably have very high 
IRT concentrations which fall with age and the progress of the 
disease, allied with the fact that heterozygotes have high concentrations, supports 
the previous suggestion that an uncontrolled hypersecretion of zymogen granules is 
the basic cellular defect in CF. 