Immunoreactive trypsin in cystic fibrosis.

Since the first observation in 1979 that CF infants have elevated blood IRT, studies in various centres have enabled us to more fully understand the importance of this phenomenon. There is increasing evidence to show that mass newborn screening for CF using the IRT assay is practical and is capable of detecting essentially all CF newborns at a cost comparable to existing screening programs for other disorders such as Hypothyroidism. Although the elevated IRT levels seen in infancy in CF soon decrease, IRT levels in older CF patients appear to quite closely reflect the capability of that patient to secrete pancreatic enzymes and can be helpful in separating CF patients whose ability to secrete enzymes is preserved, from those with diminished exocrine pancreatic function. In all CF patients there appears to be an altered relationship between pancreatic exocrine secretion and circulating IRT levels as compared to control patients. This is probably one further manifestation of a secretory obstructive defect which although not uniformly severe, is common to all CF patients.