Quantification of chloride in sweat with the Cystic Fibrosis Indicator System

We examined the relation between chloride concentration and the area of complexed chloride of Medtronic's Cystic Fibrosis Indicator System, using a high-resolution x-y coordinated digitizer to measure the circumference of the chloride precipitation ring. These digitized points were entered directly into an IBM PC computer, where the area of the chloride precipitation was calculated with use of a repetitive rectangular estimation program. Using these data, we determined the relationship between the area of chloride precipitation and the chloride concentration of the standard NaCl solutions. When the area of the ring of chloride precipitation in the system's patch is measured immediately after the sweat test is completed, the concentration of chloride in the sweat can be calculated with a reproducibility equal to that of the Gibson-Cooke sweat test.