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

Area of Science:

• Clinical Chemistry
• Pediatric Medicine
• Diagnostic Testing

Background:

• The relationship between sweat electrolytes and age is not well-established.
• The diagnostic utility of measuring sweat sodium or the chloride:sodium ratio is uncertain.

Purpose of the Study:

• To investigate the age-related variations in sweat electrolytes.
• To evaluate the discriminatory value of sweat sodium and the chloride:sodium ratio in diagnosing cystic fibrosis (CF).

Main Methods:

• Analysis of 13,785 sweat tests collected over 23 years using the Macroduct method.
• Examination of sweat chloride, sweat sodium, and chloride:sodium ratio in relation to age.

Main Results:

• Sweat chloride levels exhibit age-dependent changes, decreasing in infancy, increasing until the fourth decade, and then stabilizing or slightly decreasing.
• Sweat sodium showed overlap between positive and negative tests in children but not in adults.
• A higher chloride:sodium ratio (>1) was more likely with a positive sweat test, but most individuals with a ratio >1 did not have CF.

Conclusions:

• Sweat chloride and sodium concentrations are influenced by age.
• Measuring sweat sodium alone does not enhance diagnostic value.
• The prevalence of a chloride:sodium ratio >1 varies significantly across different age groups, impacting its utility in CF diagnosis.