Sweat Chloride Testing
At a Cystic Fibrosis Foundation GAP Conference on the sweat test, it was stated that "the diagnosis of cystic fibrosis must include a carefully performed quantitative pilocarpine iontophoretic sweat test which is interpreted by an experienced clinician." In the presence of clinical symptoms such as recurrent respiratory disease or malabsorption, a family history of cystic fibrosis (CF), or a positive newborn screen, the findings of a sweat chloride above 60 mmol/L (for children) is consistent with the diagnosis of CF. A positive test should always be confirmed. Borderline is 40-60 mmol/L and always warrants repetition of the test. A negative test should be repeated if the clinical picture is suggestive of CF.
The purpose of this collection of web pages is to provide a state-of-the-art, practical description of the Gibson-Cooke Quantitative Pilocarpine Iontophoresis Sweat Test. We provide a step by step description of sweat stimulation, collection of sweat on filter paper, elution of sweat, and analysis of sweat chloride by the coulometric titration of chloride with silver by a digital chloridometer. Common errors in sweat testing are also highlighted.
This web site is meant to be a resource for laboratories that are conducting sweat tests. Patients or parents who have questions should direct those questions to their physician. (If patients or parents submit questions to Dr. Michael Rock, the question WILL NOT be answered.)
This protocol should be considered an adjunct to the National Committee for Clinical Laboratory Standards (NCCLS) document on sweat testing (Sweat Testing: Sample Collection and Quantitative Analysis; Approved Guideline. NCCLS document C34-A2, Vol. 20 No. 14 (ISBN 1-56238-407-4) NCCLS, 940 West Valley Road, Suite 1400, Wayne, Pennsylvania, 19087-1898, USA, 2000.)