Limitations of faecal elastase-1 and chymotrypsin as tests of exocrine pancreatic disease in adults

Background: The faecal enzymes elastase and chymotrypsin are a relatively inexpensive non-invasive means of investigating causes of malabsorption. However, such tests may be affected by enzyme degradation or faecal dilution. Methods: Faecal elastase-1 and chymotrypsin were measured in 225 patients in whom pancreatic disease was suspected, and the association between faecal free water and pH with these faecal enzymes was examined in subjects with normal pancreatic function. Results: The sensitivity of faecal elastase-1 and chymotrypsin for identifying exocrine pancreatic disease was 75% and 60%, respectively. Corresponding specificities for excluding disease were 95% and 97%. The positive predictive value for faecal elastase-1 increased from 58% to 92% when watery diarrhoea was excluded. Faecal elastase-1 (inversely) and chymotrypsin (directly) were significantly associated with percentage faecal free water content in subjects without pancreatic disease. Faecal elastase-1 was not related to faecal pH, whereas chymotrypsin was inversely related to pH. Conclusion: Faecal elastase-1 is a more sensitive test for exocrine pancreatic disease in adults but is affected by dilution in patients with watery diarrhoea. The value of faecal chymotrypsin is limited by intestinal degradation.