Sweat conductivity test: Can it replace chloride titration for cystic fibrosis diagnosis?

摘要

Although sweat conductivity values are well matched with chloride concentrations for cystic fibrosis (CF) diagnosis, sweat conductivity is not accepted as a definitive diagnostic tool but only a screening method. The aim of this study was to compare the sweat chloride measurements and sweat conductivity values of our patients, and to determine cut-off values of conductivity for making or excluding a CF diagnosis. Fifty-nine CF patients, 10 patients with elevated sweat tests and 69 non-CF patients were included in the study. The mean conductivity values were 123 (64-157) mmol/L, 75.1 (60-93) mmol/L and 39 (18-83) mmol/L in the CF, elevated sweat test and control groups, respectively. The mean chloride concentration values were 107.5 (35-166) mEq/L, 48 (42-76) mEq/L and 25 (11-39) mEq/L in the CF, elevated sweat test and control groups, respectively. Spearman correlation test determined a strong correlation between conductivity and chloride concentration values (r=88%, p<0.001) in all subjects. According to the receiver operating characteristic (ROC) curve graph, the best conductivity cut-off value to make the CF diagnosis was found to be 90 mmol/L and to exclude the CF diagnosis was 70 mmol/L. We suggest that the conductivity measurement is as reliable as quantitative sweat chloride analysis to diagnose or exclude CF, and it can be used as a diagnostic test in addition to screening.