Sweat Testing: Sample Collection and Quantitative Chloride Analysis; Approved Guideline
|Publication Date:||1 December 2009|
The following procedures are described: the stimulation and collection of sweat and the quantitative measurement of chloride; sweat stimulation by pilocarpine iontophoresis (specific precautions are noted); and sweat collection in filter paper, gauze, and microbore tubing. Sweat chloride (Cl−) determination is described using coulometric titration. Screening methods based on sweat conductivity are also mentioned. Other methods for measuring sweat electrolytes after pilocarpine iontophoresis exist but are not included in the guideline. Some of these methods are documented as having significant analytical problems and also have limited diagnostic application.3-8 Validation studies and quality assurance (QA) techniques are discussed, along with analytical and biological sources of error. The evaluation of sweat chloride test results to include reference intervals and diagnostic criteria are described, with an emphasis on the application of sweat chloride testing to newborn screening for cystic fibrosis (CF). This document is primarily directed towards laboratory and clinical personnel responsible for collecting, analyzing, reporting, and evaluating sweat chloride test results.
Because the sweat test has been reported to have unacceptably high false-positive and false-negative rates attributable to inaccurate methodology, technical error, and patient physiology,3-8 comprehensive guidelines addressing the collection of sweat and the quantitative measurement of chloride in sweat are needed. Improvement in the performance of such tests can only occur when laboratory scientists and clinicians are aware of appropriate methods of collection and analysis, quality control (QC), and evaluation of results. This document describes, in detail, the quantitative pilocarpine iontophoresis test for the determination of sweat chloride, including techniques to minimize the potential for false-positive and false-negative test results.