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SUMMARY: Cinel G, Dogru D, Yalçin E, Ozçelik U, Gürcan ?, Kiper ?. Sweat conductivity test: can it replace chloride titration for cystic fibrosis diagnosis? Turk J Pediatr 2012; 54: 576-582.
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%, ? < 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.
Key words: cystic fibrosis, diagnosis, sweat conductivity, sweat chloride concentration.
According to the Cystic Fibrosis Foundation, diagnostic criteria for cystic fibrosis (CF) are based on the presence of clinical phenotypic features of the disease and the evidence of cystic fibrosis transmembrane regulator (CFTR) dysfunction. The dysfunctional CFTR can be demonstrated by identification of mutations in both alleles of the CF gene, abnormal nasal potential difference, or elevated sweat chloride concentrations on two different occasions1'3. Currently, the sweat test is the most widely used method for CF diagnosis.
Measurement of sweat chloride concentration by the quantitative pilocarpine iontophoresis test (QPIT) was firstly described by Gibson and Cooke4, and it has been used as the most reliable method for CF diagnosis and has been accepted as...