Fecal elastase-1 determination:: 'Gold standard' of indirect pancreatic function tests?

Background: Tubeless pancreatic function tests measuring the content of elastase-1 and the activity of chymotrypsin in stool are used with different cut-off levels and with varying success in diagnosing functional impairment of the pancreas. The aim of our study was to re-evaluate the sensitivity and specificity of elastase-1 and chymotrypsin in stool in the assessment of exocrine pancreatic insufficiency. Methods: In 127 patients displaying clinical signs of malassimilation, the secretin-caerulein test ('gold standard'), fecal fat analysis, fecal chymotrypsin activity and fecal elastase-1 concentration were performed. Exocrine pancreatic insufficiency was graded, according to the results of the secretin-caerulein test, into mild, moderate and severe. Chymotrypsin and elastase-1 in stool were estimated using two commercially available test kits. Fecal elastase-1 concentration of 200 and 100 mug/g stool and chymotrypsin activity of 6 and 3 U/g stool were used separately as cut-off levels for calculation. Results: 1) In 65 patients, a normal pancreatic function was found using the secretin-caerulein test. In 62 patients, an exocrine pancreatic insufficiency was found and classified into severe (n = 25), moderate (n = 14) and mild (n = 23). 2) The correlation between fecal elastase-1 and chymotrypsin with duodenal enzyme outputs of amylase, lipase, trypsin, chymotrypsin and elastase-1 ranged between 33% and 55% and 25% and 38%, respectively. 3) Using a cut-off of 200 mug elastase-1/g, stool sensitivities of fecal elastase- I and fecal chymotrypsin (cut-off; 6 U/g) were 100% and 76%, respectively (P < 0.0001 and P < 0.001 respectively) in severe exocrine pancreatic insufficiency, 89% and 47% respectively (P < 0.001; P = 0.34, respectively) in moderate and 65% for both in mild pancreatic insufficiency. Specificities of elastase-1 and chymotrypsin in stool were 55% and 47%, respectively. 4) Elastase-1 based diagnostic provided a positive predictive value of 50% using a 'cut-off' 200 mug/g stool in a representative group of consecutively recruited patients with gastroenterological disorders. Conclusion. Determination of fecal elastase-1 is highly sensitive in the diagnosis of severe and moderate exocrine pancreatic insufficiency and is of significantly higher sensitivity than fecal chymotrypsin estimation. Specificity for both stool tests is low. Correlation between elastase-1 and chymotrypsin in stool and duodenal enzyme outputs is moderate. Neither test is suitable for screening, as they provide a pathologic result in roughly half of 'non-pancreas' patients.