Does the Macroduct® collection system reliably define sweat chloride concentration in subjects with intermediate results?

Abstract: Objectives: The sweat test remains the current diagnostic gold standard for CF disease. Many CF testing centres have switched from the Gibson and Cooke to the Macroduct®. Since the validity and sensitivity of Macroduct® has not been tested in patients with intermediate sweat chloride concentrations, we compared both methods simultaneously including subjects expected to have intermediate results. Design and methods: We prospectively evaluated controls, obligate heterozygotes, patients with CF and with an uncertain diagnosis of CF (congenital absence of the vas deferens, pancreatitis and sinopulmonary disease). Results: We assessed 82 subjects (3.7–60.1 years); 14 healthy controls, 7 obligate heterozygotes, 20 CF (15 pancreatic insufficient, 5 pancreatic sufficient), and 41 with unproven diagnosis. Mean test difference was close to 0 (95% CI±20 mmol/L) and test values were highly correlated (r =0.93, p ≤0.0001). Discrepancies between the two testing methods occurred in 22% of subjects. Conclusion: Sweat chloride measured by Macroduct® highly correlates with Gibson and Cooke for concentrations in all ranges, including the intermediate range. This study reveals the limitations of sweat testing for excluding a diagnosis of CF since 38% of subjects had intermediate range results. [Copyright &y& Elsevier]