Protein-losing enteropathy in dogs is associated with decreased fecal proteolytic activity

Background: Measurement of proteolytic activity in feces is a traditional method for the diagnosis of exocrine pancreatic insufficiency (EPI). A drawback of this method is the occurrence of falsely low results that may lead to a false-positive diagnosis of EPI. We hypothesized that intestinal loss of serum proteinase inhibitors in protein-losing enteropathy (PLE) may inhibit fecal proteolytic activity and be a potential source of false low results. Objective: The objective of this study was to determine the effect of PLE on fecal proteolytic activity in dogs. Methods: Fecal proteolytic activity was measured using a radial diffusion casein digestion assay in 12 samples from 4 clinically healthy control dogs and 30 samples from 16 dogs with PLE. Gastrointestinal protein loss was assessed using an ELISA to determine fecal canine α₁-proteinase inhibitor concentration. The relationship between the concentration of canine α₁-proteinase inhibitor in the feces and the diameter cleared in the casein digestion assay was determined. The mean clearing diameter was compared between control dogs and dogs with PLE. Results: A significant negative correlation was observed between fecal canine α₁-proteinase inhibitor concentration and casein clearing diameter (P < .001, Pearson r= -.6317, r² =.3999). Mean clearing diameter was significantly lower in dogs with PLE than in control dogs (12.63 vs 16.83 mm, P < .001, two-tailed Student's t-test). Conclusion: Increased fecal loss of α₁-proteinase inhibitor in dogs with PLE is associated with a significant decrease in fecal proteolytic activity and may result in a false positive diagnosis of EPI.