Comparison between classic Gibson and Cooke technique and sweat conductivity test in patients with and without cystic...

To compare sweat chloride values obtained by quantitative pilocarpine iontophoresis (classic test) with the sweat conductivity values obtained using Macroduct collection system in patients with and without cystic fibrosis (CF). The cost and time spent to carry out each test were also analyzed.

The sweat test using both techniques was performed at the same time in patients with and without CF. Conductivity cutoff values to rule out or diagnose CF were < 75 and > or = 90 mmol/L, respectively, and for the classic test the chloride values were < 60 and > or = 60 mmol/L.

Fifty-two patients with CF (29 males and 23 females; aged from 1.5 to 18.2 years) underwent the sweat test using both techniques, showing median sweat chloride and conductivity values of 114 and 122 mmol/L, respectively. In all of them, conductivity was > or = 95 mmol/L, which provided the test with 100% sensitivity (95%CI 93.1-100). Fifty patients without CF (24 males and 26 females; aged from 0.5 to 12.5 years) had median sweat chloride and conductivity values of 15.5 and 30 mmol/L, respectively. In all cases, conductivity was < 70 mmol/L, which provided the test with 100% specificity (95%CI 92.9-100). Time spent to perform the tests was significantly shorter for the conductivity test, and its cost was also lower.

The conductivity test showed high sensitivity and specificity, and there was good correspondence between the tests. The time spent to carry out the conductivity test was shorter and the cost was lower in comparison with the classic test.