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Relationship between sweat chloride, sodium, and age in clinically obtained samples

  • Researchers

    Traeger N, Shi Q, Dozor AJ.

  • Place of research

    New York Medical College, Department of Pediatrics & The Armond V. Mascia, MD Cystic Fibrosis Center of the Maria Fareri Children's Hospital at Westchester Medical Center, Valhalla, New York, USA

  • Publication

    Journal of Cystic Fibrosis, August 2013

  • Subjects

    ,

  • How do the chloride and sodium levels in sweat vary with age, and does measuring sweat sodium, or calculating the chloride: sodium ratio help in interpreting sweat tests?

  • Why is this important?

    The sweat chloride test remains critical to making a diagnosis of Cystic Fibrosis (CF). Since the amount of chloride in sweat varies with age, this study provides more information regarding what values should be considered abnormal. It has been suggested that sweat chloride is usually greater than sweat sodium in patients with CF, and the reverse is true in those without CF.

  • What did you do?

    We reviewed the results of 14,392 sweat tests performed between 1986 and 2009, analyzed how sweat chloride and sodium varied with age, and examined the value of the chloride:sodium ratio.

  • What did you find?

    Sweat chloride tended to decrease over the first year of life, slowly increase until the fourth decade, then either level off or slightly decrease. Measuring sweat sodium did not add much. 54% of patients with sweat tests diagnostic for CF had a chloride:sodium ratio > 1, but only 8% of subjects with a chloride:sodium ratio > 1 had a positive sweat test. This ratio and the proportion of patients with an elevated ratio varied dramatically between age groups.

  • What does this mean and reasons for caution?

    Perhaps currently recommended sweat chloride cut-off values are not appropriate for all age groups. However, only patients referred for sweat tests were studied, not truly healthy controls; and relatively fewer older adults were included.

  • What's next?

    Our findings should be confirmed by a large prospective study with healthy controls, particularly focusing on older adults. Understanding physiological differences between infants, children and adults might lead to improved understanding of CFTR dysfunction at a basic level and improve our ability to diagnose and treat patients with CF.