Biological variability of the sweat chloride in diagnostic sweat tests: A retrospective analysis

Abstract Background The sweat test is the current gold standard for the diagnosis of cystic fibrosis (CF). CF is unlikely when sweat chloride (Clsw ) is lower than 30 mmol/L, Clsw > 60 is suggestive of CF, with intermediate values between 30 and 60 mmol/L. To correctly interpret a sweat chloride...

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Bibliographic Details
Published in:Journal of cystic fibrosis 2017-01, Vol.16 (1), p.30-35
Main Authors: Vermeulen, F, Lebecque, P, De Boeck, K, Leal, T
Format: Article
Language:English
Subjects:
Age Distribution
Belgium
Biological Variation, Population
Child
Chlorides - analysis
Cystic fibrosis
Cystic Fibrosis - diagnosis
Diagnosis
Diagnostic Tests, Routine - methods
Diagnostic Tests, Routine - standards
Female
Humans
Infant
Male
Pulmonary/Respiratory
Reference Values
Retrospective Studies
Sweat - chemistry
Variability
Young Adult
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Summary:Abstract Background The sweat test is the current gold standard for the diagnosis of cystic fibrosis (CF). CF is unlikely when sweat chloride (Clsw ) is lower than 30 mmol/L, Clsw > 60 is suggestive of CF, with intermediate values between 30 and 60 mmol/L. To correctly interpret a sweat chloride value, the biological variability of the sweat chloride has to be known. Methods Sweat tests performed in two centers using the classic Gibson and Cooke method were retrospectively reviewed (n = 5904). Within test variability of Clsw was measured by comparing results from right and left arm collected on the same day. Between test variability was calculated from subjects with sweat tests performed on more than one occasion. Results Within test variability of Clsw calculated in 1022 subjects was low with differences between − 3.2 (p5) and + 3.6 mmol/L (p95). Results from left and right arm were classified differently in only 3 subjects. Between test variability of Clsw in 197 subjects was larger, with differences between − 18.2 mmol/L (p5) and + 14.1 mmol/L (p95) between repeat tests. Changes in diagnostic conclusion were seen in 55/197 subjects, the most frequent being changing from indeterminate to ‘CF unlikely’ range (48/102). Conclusion Variability of sweat chloride is substantial, with frequent changes in diagnostic conclusion, especially in the intermediate range.
ISSN:1569-1993
1873-5010
DOI:10.1016/j.jcf.2016.11.008