Chloride sweat

Keywords: Electrolyes - sweat, Electrolytes sweat, Sweat electrolytes

Specimen:

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

Method:

ISE, spectrophotometry, coulometry, ICP-MS.

Reference Interval:

Decision limits:

0-6 months:
= or < 29 mmol/L normal,
30-59 mmol/L intermediate,
= or > 60 mmol/L supportive of CF.

> 6 months – 18 years:
= or < 39 mmol/L normal,
40-59 mmol/L intermediate,
= or > 60 mmol/L supportive of CF.

Values are higher in adults - consult pathologist.

Application:

Diagnosis of Cystic fibrosis.

Interpretation:

Levels > 60 mmol/L are supportive of Cystic fibrosis but the finding should be confirmed on a second collection.

The test should be repeated if levels are 30-59 (= or < 6 months) or 40-59 mmol/L (> 6 months) as Cystic fibrosis, particularly mild variants, is not excluded. In these cases CFTR genotyping may be informative.

Some mild variants of Cystic fibrosis may show normal sweat electrolyte levels.

See also Cystic fibrosis.

Reference:

CLSI. Sweat Testing: Sample Collection and Quantitative Chloride Analysis: Approved Guidelines – Third Edition. CLSI Document C34-A3. Wayne, PA: Clinical and Laboratory Standards Institute, 2009.