The sweat test for quantitation of electrolytes - A challenge in precision

The sweat test, a quantitative analysis of electrolytes in sweat, is the most valuable and widely used laboratory test for the diagnosis of cystic fibrosis. Despite its importance, this test is performed in only 19% of US laboratories, according to a recent survey by the college of American Pathologists. The sweat test's reliability may be in jeopardy owing to several factors, including a lack of uniformity in the preanalytic pilocarpine iontophoresis stimulation and subsequent sweat collection, and in the analytic procedures for sweat electrolytes. This article reviews the quantitative analysis of sweat electrolytes, with emphasis on quality assurance and accuracy of techniques.