Chloride - sweat

Minimum of 100 mg of sweat collected by the standard sweat test (pilocarpine iontophoresis is the preferred method).

<40 mmol/L (children).

Values are higher in adults - consult pathologist.

Levels >60 mmol/L are diagnostic of cystic fibrosis although the finding should be confirmed on a second collection.

The test should be repeated if levels are 40-60 mmol/L as cystic fibrosis, particularly mild variants, is not excluded. In these cases CFTR genotyping may be informative.

Sweat sodium should be measured as confirmation of chloride results.

Some mild variants of cystic fibrosis may show normal sweat electrolyte levels.
See also Cystic fibrosis under Molecular genetics - individual genetic disorders.