Reliability of sweat test in cystic fibrosis [letter].

The report by Huff, Huang, and Arey again calls attention to the 
heterogeneity of cystic fibrosis and to the fact that a properly 
performed sweat test in the normal or borderline range does not 
rule out cystic fibrosis. This may occur in approximately 1% of 
patients we classify as having cystic fibrosis and confirms our original 
impression that the sweat test has a reliability of between 98% 
and 99%. One must pay close attention to the clinical picture, 
the family history, and especially the pulmonary or gastrointestinal findings, and 
provide rational treatment until more acceptable evidence of the disease can 
be documented. In the same issue is a report on a 
false positive sweat test in a Canadian patient with the Mauriac 
syndrome. The authors list a variety of conditions that have been 
reported as yielding elevated sweat electrolytes. The manner of the collections 
can greatly influence the result. - In patients with transient abnormal 
sweat electrolytes, sodium values were consistently higher than chloride values. Perhaps 
the finding of sodium values in excess of chloride in the 
abnormal range suggests a false positive test. 