Cystic fibrosis is caused by defects in a protein found in many tissues, including the airways and the sweat glands.
What remains is sweat, a salt solution with a relatively finely tuned concentration of sodium and chloride.
[3] At the test site, an electrode is placed over gauze containing pilocarpine and electrolyte solution that will not interfere with the sodium and chloride measurement.
Because of the existence of milder variants, borderline or even near-borderline negative results may be used to diagnose CF.
Clinical presentation, family history and patient age must be considered to interpret the results.
Technical errors, insufficient sample, evaporation, contamination, dehydration, mineralocorticoid hormone therapy, and skin rash on the tested area may produce incorrect results.
Positive test results may also be caused by malnutrition, adrenal insufficiency, glycogen storage diseases, hypothyroidism, hypoparathyroidism, nephrogenic diabetes insipidus, G6PD deficiency or ectodermal dysplasia.