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Correspondence to Professor Paulo Camargos, Pediatrics, Universidade Federal de Minas Gerais, Belo Horizonte 31270-901, Brazil; [email protected]
WHAT IS ALREADY KNOWN ON THIS TOPIC
Sweat conductivity (SC) is considered a screening test for cystic fibrosis (CF); there is no systematic review and meta-analysis comparing SC with sweat test to verify its role as an alternative method to rule in/rule out CF.
WHAT THIS STUDY ADDS
SC demonstrated an excellent pooled diagnostic accuracy for CF.
HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY
In settings with a shortage of sweat tests, SC can expedite diagnosis and allow prompt treatment.
Introduction
Sweat chloride determination using coulometric titration has been widely accepted as the gold standard for cystic fibrosis (CF) diagnosis but requires a specialised centre and skilled technicians. As sweat collection through Macroduct coils is expensive, sweat chloride determination using the Gibson and Cooke procedure is the preferred strategy in limited-resource settings.
Sweat conductivity (SC) has a long history that started even before the description of the quantitative pilocarpine iontophoresis by Gibson and Cooke in 1959. In 1957 and early 1960s, Dr Harry Shwachman, chief of the Division of Clinical Nutrition at Children’s Hospital, Boston, assessed the reliability of SC in three articles.1–3
Shwachman and his colleagues stated that electrical conductivity measurement was practical and highly sensitive. In addition, they observed that the electrical conductance of an electrolyte solution is a function of several variables: the species and concentration of ions present in the solution, and the temperature and the geometry of the conductivity cell. The elemental sweat composition includes inorganic (sodium, potassium, chloride and calcium and sulfate) and organic (lactic acid, urea and amino acids as nitrogen) constituents. If a constant temperature and a given conductivity cell are employed, the conductance becomes a measure of the kind and concentration of the ions present. Moreover, they pointed out that the conductivity of a multicomponent electrolyte solution is equal to the sum of the conductivities of its ions. Therefore, it would be logical to assume that the conductivity elevation in patients with CF is mainly due to the increased sodium chloride content. In brief, they reported that increased conductivity paralleled increasing chloride concentrations and concluded that SC separated patients with CF from controls.1–3
Again, in 1967,...