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

Abstract

Background: The relationship between sweat electrolytes and age is uncertain, as is the value of measuring sodium or the chloride:sodium ratio.

Methods: 13,785 sweat tests performed over 23 years at one center through the Macroduct collection in clinically obtained samples were analyzed.

Results: Sweat chloride tended to decrease over the first year of life, slowly increase until the fourth decade, then either level off or slightly decrease. In children, sweat sodium overlapped between those with positive and negative sweat tests, but not in adults. If the sweat test was positive, there was a higher likelihood of having a chloride:sodium ratio >1, but most subjects with a ratio >1 did not have CF.

Conclusions: Sweat chloride and sodium vary with age. Measurement of sweat sodium did not add discriminatory value. The proportion of subjects with a chloride:sodium ratio >1, with or without CF, varied greatly between age ranges.

Keywords: Cystic fibrosis; Electrolytes; Newborn screening; Sweat.