FALSELY positive tests for fecal trypsin due to bacterial gelatinase 1 were found for more than one-half of 137 children2 with cystic fibrosis of the pancreas whose feces were tested by the x-ray-film technique.3 Previous studies4 have indicated that soybean trypsin inhibitor will inhibit gelatin liquefaction due to pancreatic trypsin and pancreatin-U.S.P. but not that due to bacterial gelatinase. The reliability and consistency of results obtained by the "spot film" technique for fecal trypsin are affected by the following factors: (1) The pH of the fecal suspension1 (2) Age of the specimen (3) Consistency of the stool (4) Differences in the type of x-ray and photographic film used in the test5 (5) Presence of barium and certain other heavy metal ions in high concentration in the fecal specimen6 (6) Temperature at which the fecal suspension is incubated on the x-ray film (7) Presence of bacterial gelatinase7
JOHNSTONE DE. STUDIES ON CYSTIC FIBROSIS OF THE PANCREAS: Role of Various Diluents and the Dilution Factor in the Interpretation of the X-Ray-Film Test for Fecal Trypsin. AMA Am J Dis Child. 1952;84(2):191–198. doi:10.1001/archpedi.1952.02050020055006
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