Sweat chloride test

Summary A 3-year-old Caucasian male has a history of chronic pulmonary and gastrointestinal problems and has a positive chloride sweat test. A family history of similar symptoms is also present. 

Diagnosis of CF is based on two separate elevated sweat chloride concentrations of greater than or equal to 60 mEq/L (or mmol/L) obtained through pilocarpine iontophoresis (referred to as the sweat test ). Genetic testing (CFTR mutation analysis) may be performed to confirm the diagnosis, screen in utero, or detect carrier status. More than 70% of diagnoses are made by 12 months of age and almost all are made by age 12. 

T. Bray, G. C. F. Clark, G. J. Moody and J. D. R. Thomas, A Perspective of Sodium and Chloride Ion-Selective Electrode Sweat Tests for Screening in Cystic Fibrosis, University of Wales, Cardiff (1975). 

Q2 In the sweat test, sweating is induced by passing a weak electric current across an area of skin treated with the secretory stimulant pilocarpine. The current enhances the ability of pilocarpine to penetrate skin and so local secretion of sweat is induced. When this test was performed on Carmen, the diagnosis was confirmed her sweat was found to contain 100 mmol l-1 chloride, normally this is expected to be <60 mmoll-1. 

The sweat test occurs in three phases sweat stimulation by pilocarpine iontophoresis collection of the sweat onto gauze, filter paper, coil, patch, or capillary tube and qualitative or quantitative analysis of sweat chloride, sodium, conductivity, or osmolality. A survey of 753 laboratories (Table 27-3) performing sweat testing revealed that 47% analyze chloride, 46% analyze conductivity, and less than 7% analyze sodium or osmolality. ... 

High sweat chloride levels are found in patients with cystic fibrosis (see sweat test). 

Ion-selective electrodes. These have particularly useful applications in the determination of sWeat chloride in cystic fibrosis see sweat test). 

Although most patch testing is done with nickel sulfate because it is less irritating than nickel chloride, exposure of the skin to nickel alloys results in the release of nickel chloride from the influence of human sweat. Therefore, nickel chloride is the more relevant form of nickel for examining threshold concentrations (Menne 1994). Menne and Calvin (1993) examined skin reactions to various concentrations of nickel chloride in 51 sensitive and 16 nonsensitive individuals. Although inflammatory reactions in the sweat ducts and hair follicles were observed at 0.01% and lower, positive reactions to nickel were not observed. To be scored as a positive reaction, the test area had to have both redness and infiltration, while the appearance of vesicles and/or a bullous reaction were scored as a more severe reaction. At 0.1%, 4/51 and 1/51 tested positive with and without 4% sodium lauryl sulfate. Menne et al. (1987) examined the reactivity to different nickel alloys in 173 nickel-sensitive individuals. With one exception (Inconel 600), alloys that released nickel into synthetic sweat at a rate of <0.5 pg/cmVweek showed weak reactivity, while alloys that released nickel at a rate of >1 pg/cm /week produced strong reactions. 

Finally, the electrode configuration was tested with artificial sweat instead of sodium chloride-containing electrolyte solutions. No shifts of relationships or different results were found between the experiments performed with artificial sweat and those with sodium chloride solutions (section 10.4). From these results, the following conclusions can be drawn ... 

The ease of application, the minimization of systemic side effects, and the increased drug penetration directly into the target region resulted in extensive clinical use of iontophoresis mainly in the transdermal field. This technique has been utilized for administration of local anesthetics [2-5], sweat chloride testing in cystic fibrosis patients by transcutaneous delivery of pilocarpine [6,7], administration of vidarabine to patients with herpes orolabialis [8], fluoride administration to patients with hypersensitive dentin [9,10], and gentamicin delivery for the management of burned ears [11],... 

Many errors can occur during the collection, processing, and transport of biological specimens. Minimizing these errors win result in more reliable information for use by healthcare professionals. Examples of biological specimens that are analyzed in clinical laboratories include whole blood serum plasma urine feces saliva spinal, synovial, amniotic, pleural, pericardial, and ascitic fluids and various types of solid tissue. The National Committee for CMnical Laboratory Standards (NCCLS) has published several procedures for collecting many of these specimens under standardized conditio ns.In addition, the NCCLS has published documents related to sample collection and analysis for specialized tests, such as sweat chloride (see also Chapter 27). 

There is a lack of consensus on the appropriate decision limit for sweat conductivity. The CFF states that a patient with a sweat conductivity >50 mmol/L should be referred for a confirmatory sweat chloride test, and Wescor recommends that conductivity values up to 60 mmol/L can be considered normal, and concentrations >80 mmol/L are positive for... 

W Ion selective electrodes can have many diagnostic applications in biology. For example, the chloride electrode is being used to assay chloride ion activity in the sweat of babies as a diagnostic test for cystic fibrosis. Another application with a potential for direct health use falls in the area of dental research. Calcium and fluoride electrodes are being used to study the relationship between tooth decay and saliva ion composition. 

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