Abnormalities of circulating immunoreactive pancreatic anionic trypsinogen in cystic fibrosis: an assay artifact due to cross-reacting serum antibodies.

In patients with CF, serum pancreatic cationic trypsinogen has proven to be useful for newborn diagnostic screening and also as a test of pancreatic function in the older patient. However, an assay for serum anionic trypsinogen is of no value as a test of pancreatic function in CF due to an apparent artifactual elevation of this enzyme in some patients. In this study, we evaluated the extent of the abnormality in the anionic trypsinogen assay and also elucidated the nature of the interfering material. CF patients were grouped according to the presence (pancreatic insufficiency) or absence (pancreatic sufficiency) of steatorrhea. In CF infants, both serum cationic and anionic trypsinogen levels were greatly elevated. Serum cationic trypsinogen declined with age in patients with pancreatic insufficiency, reaching low or undetectable levels after 6 years. In contrast, serum anionic trypsinogen levels remained normal or elevated in 33% of those over 6 years of age. There was no age-related change in either cationic or anionic trypsinogen among the CF patients with pancreatic sufficiency, and the majority had normal or elevated levels. Serum samples from selected CF patients were separated into IgG and non-IgG fractions using Staph. Protein A columns. Immunoreactive cationic and anionic trypsinogen were detectable in the non-IgG fractions of sera from CF infants and older patients with pancreatic sufficiency. In older CF patients with undetectable serum cationic and anionic trypsinogen, no immunoreactive material was detectable in either the IgG or non-IgG fractions.(ABSTRACT TRUNCATED AT 250 WORDS)