The sweat test: sodium and chloride values.

THE IMPORTANCE of establishing a correct diagnosis of cystic fibrosis requires little discussion. Since this is a life-long disease characterized by a series of complications with increasing age, it is imperative not to overdiagnose and thus provide expensive, complicated, and restrictive therapy. On the other hand, to fail to make the diagnosis in a sick child may hasten his death. Errors in diagnosis also have serious genetic implications and may result either in restricting family size or adding more affected children. A positive sweat test by itself does not establish the diagnosis of cystic fibrosis. The reliability of the sweat test, the best method, and details of the procedure have been the subject of numerous publications? -a Unfortunately, the sweat test, whether performed by the recommended method or by other methods, has been shown to be unreliable in many instances. "-~ The first authoritative publication by the Cystic Fibrosis Foundation recommended the pilocarpine iontophoresis quantitative method devised by Gibson and Cooke? We have adopted this method of stimulating sweat production, and measure sodium, potassium, and chloride in the induced sweat sample. One would expect the values for sodium and chloride to be in the same range. Should the values differ greatly, one might question the reliability of the determination. There appears to be no special advantage of measuring either sodium or chloride in diagnostic testing. The values for chloride tend to be slightly higher than those for sodium in patients with cystic fibrosis, whereas the reverse tendency occurs in control subjects. This report will present an analysis of our findings in examining 252 patients with cystic fibrosis and 252 controls. This study whs designed to determine whether Na or C1 is the preferred single measurement, to determine the relationship of Na to C1, and to define what