Screening for cystic fibrosis by a stool trypsin method.

Mass screening for cystic fibrosis by a trypsin assay of stool dried on filter paper was evaluated in 20 000 5-day-old babies. Sweat tests were required in only 7 babies. Three of them had cystic fibrosis. The test gave a false-negative result in at least 2 babies, but each had normal pancreatic function. This is not an ideal screening test for cystic fibrosis, as it misses cases with normal pancreatic function, but it is very cheap, highly specific, and appears to be the best currently available screening test.