Sweat Test for Cystic Fibrosis
Reviewed
This test measures the amount of chloride in sweat to help diagnose cystic fibrosis (CF). It is often performed on newborns after a positive screening or on individuals of any age with symptoms of CF or a family history of the disease.
Preparation and collection
Avoid applying creams or lotions to the skin for 24 hours before the test.
Understanding this test
Use the reference interval and units printed by the laboratory that performed the test. A result outside that interval is not a diagnosis by itself, and a result inside it does not rule out every condition. Your symptoms, history, medicines, timing, and related tests can change what the result means.
- A normal sweat chloride level (<29 mmol/L) does not completely rule out cystic fibrosis; some people with CF have normal results.
- A positive sweat chloride level (≥60 mmol/L) may rarely be caused by conditions other than CF, such as hypothyroidism, nephrogenic diabetes insipidus, or Addison disease.
- Results between 30 and 59 mmol/L are considered borderline and require further testing.
- There is no known risk from the sweat test itself; the electrical current may cause a mild tingling or warmth.
What to do next
Based on the results, your healthcare provider may recommend repeating the sweat test, genetic testing, or other evaluations to confirm or rule out cystic fibrosis.
Evidence source
U.S. National Library of Medicine: Sweat Test for Cystic Fibrosis