3.6　Stool Tests

Fecal excretion of pancreatic enzymes correlates with duodenal enzyme secretion（Katschinski et al.1997），and，compared with other enzymes，elastase-1 and chymotrypsin are very stable during intestinal transit.Therefore，these two enzymes appear suitable for stool testing.

The concentration of fecal elastase-1 in the stool sample is stable and cannot be influenced by pancreatin supplements，accordingly there is no need to discontinue pancreatic enzyme preparations，thus the measurement of fecal elastase-1 is the preferred and best available pancreatic function test.While the exact threshold depends on the method used for evaluation，normal stool concentration of elastase-1 usually exceeds 200 µg/g.Less than 100 µg/g stool are usually equivalent to severe pancreatic exocrine insufficiency.However，the diagnostic value is limited in early stages of chronic pancreatitis as the sensitivity is only 54-75%in mild to moderate pancreatic exocrine insufficiency（Hoffmeister et al.2012）.Moreover，specificity of fecal elastase-1 is rather low in the differential diagnosis of diarrhea，because stool dilution by increased stoolwater content artificially decreases elastase-1 concentration（Keller et al.2009）.(https://www.daowen.com)

The activity of chymotrypsin in stool can be tested photometrically，but sensitivity and specificity are even lower than that of fecal elastase-1（Siegmund et al.2004）.Pancreatin supplementation needs to be discontinued at least 5 days as it is impossible to identify human and substituted porcine chymotrypsin，unless the chymotrypsin test is used to monitor a patient's compliance with enzyme supplementation in refractory cases.Three stool samples are needed for sensitivity improvement and this further explains why fecal elastase-1 measurements have mostly replaced chymotrypsin measurements nowadays.