Cystic fibrosis. Problems encountered with sweat testing.

The sweat test is the only practical and reliable laboratory test for 
confirmation of the diagnosis of cystic fibrosis. Among 234 patients referred 
to The Johns Hopkins Hospital for sweat testing, 62 had had 
a previous test; 29 tests had been reported as negative, and 
33 tests had been reported as positive. Results of quantitative pilocarpine- 
iontophoresis sweat tests at this center led to a change in 
diagnosis in 27 (43.5%) of these 62 patients. Most of the 
errors were false- positive. 