Serum isoamylase activities in cystic fibrosis patients, determined by an inhibitory assay.

Serum isoamylase activities were determined in patients with either cystic fibrosis (CF) or celiac disease and in age-matched healthy children by means of an inhibitory assay suitable for routine application. The percentage pancreatic isoamylase (PIA) activity was significantly decreased in CF patients when compared with that of patients with celiac disease. Cystic fibrosis patients with steatorrhea had lower absolute values of PIA activity and higher values of salivary isoenzyme activity than control individuals. There was no overlapping between values obtained from CF patients and either celiac patients or healthy individuals. These results suggest that determination of PIA activity may be a useful adjunct test for the diagnosis of CF in patients with steatorrhea.