What sweat chloride reference value is required for a positive diagnosis of cystic fibrosis (CF)?

Updated: Sep 28, 2020
  • Author: Girish D Sharma, MD, FCCP, FAAP; Chief Editor: Kenan Haver, MD  more...
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The sweat chloride reference value is less than 30 mmol/L. A value of more than 60 mmol/L of chloride in the sweat is consistent with a diagnosis of cystic fibrosis. [35]  The values of 30-60 mEq/L may represent heterozygous carriers, these carriers cannot be accurately identified with a sweat chloride test. [34]

The sweat test must be performed at least twice in each patient, preferably several weeks apart. Values of 40-60 mmol/L are considered borderline, and the test must be repeated because these values have been found to be consistent with the diagnosis in some patients with typical features.

Repeat a sweat test to confirm positive results. Repeat a sweat test with negative results if clinical features suggestive of cystic fibrosis are present. Some patients with genetically documented cystic fibrosis and typical symptoms have consistently negative results on sweat tests.

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