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Quality Assurance for Sweat Testing

Laboratories should develop a quality assurance process for sweat testing which begins with performing a sufficient volume of testing to ensure familiarity and competency with the testing procedure. Laboratories performing few sweat tests monthly should consider referring patients to a CF Care center for testing. Due to the complexity of the collection and analysis, testing should be limited to a few well-trained individuals. Competency should be monitored periodically through direct observation and individual technologist’s rate of skin reactions and QNS results should be documented and reviewed. For quality control at least two concentrations of controls should be analyzed every day when patient samples are tested. Analytical measurement ranges should be confirmed using chloride samples found in the normal population (ie, between 10 and 20 mmol/L). The upper end of the clinical reportable range is 160 mmol/L. Sweat chloride concentrations greater than 160 mmol/L are not physiologically possible and represent specimen contamination or analytical error. External proficiency testing (PT) is available for the sweat test from agencies such as the College of American Pathologists (CAP). PT should be included as part of the quality assurance process. Further discussion of method validation, techniques to minimize errors and appropriate collection and analysis procedures can be found in CLSI document C34-A3 (see "References" at the end of this course).