Sweat testing (measuring chloride concentration in sweat) remains the gold standard to confirm the diagnosis of CF, despite advances in genetic testing. Chloride concentration is elevated in the sweat of patients with CF. Sweat testing is also used to document the physiological response to drugs that target the protein defect.
There are three components to the sweat test: stimulation, collection, and analysis. There are other disorders in addition to CF which may result in increased, or transiently increased, sweat chloride concentrations but generally they are easy to distinguish from the clinical symptoms of CF.
Patients need to be at least 48 hours of age to undergo sweat testing because transient elevations in sweat electrolytes occur in newborns. In addition, to ensure adequate sweat production the patients should be physiologically and nutritionally stable, thoroughly hydrated, and free of acute illness.