Reappraisal of the chloride plate test as screening test for cystic fibrosis.

A rapid and simple screening test for detecting cystic fibrosis, described in 1956, has been used routinely for 21 years; the results during a 15-month period are compared with those using the quantitative pilocarpine iontophoresis sweat test. In the chloride agar plate test the concentration of chloride on the finger tips is evaluated accordingly to the intensity of the imprint. Readings of 2+ or less excluded cystic fibrosis in 1589 cases with only two doubtful instances, whereas 4+ readings were recorded in 198 cases of cystic fibrosis and 3+ readings in 15 cases of cystic fibrosis. In doubtful cases 4 individuals had 4+ readings and 11 had 3+ readings. This screening test does not replace the quantitative pilocarpine iontophoresis test but it does identify an individual who is likely to have the disease and who requires further tests. It is not reliable for infants aged under 2 months.