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Sweat Test

A sweat test is a test done to diagnose cystic fibrosis (CF). People with CF have an abnormal amount of salt in their sweat. The sweat test measures salt in the sweat.

How is the test done?

The sweat test is a painless test that does not require needles.

  • A small amount of a solution that causes people to sweat will be put on your child's forearm.
  • Small electrodes are placed over the solution. A very small (and safe) electrical current passes thru the electrodes, and pushes the solution into your child's sweat glands in the forearm. The electrodes are left on for five minutes. This sometimes causes a mild tingling sensation — much like a part of the arm "falling asleep."
  • After five minutes the electrodes are removed and the area is covered with gauze to absorb the sweat. The gauze stays in a place for 30 minutes and is then removed and sent to the lab.
  • The lab weighs the gauze to make sure there is enough sweat to give accurate results. Then the gauze is put into a machine and the amount of salt in the sweat is measured. The results are usually received from the lab in about two hours.


  • The sweat test is negative if the amount of salt is less than 30-40 mmol/L (millimoles per liter). The sweat test is positive if the result is more than 60 mmol/L.
  • If your child has a positive sweat test result, a second test will be done to double-check the value.
  • If two sweat test results are positive then a child has cystic fibrosis. That child will be seen on a regular basis in the CF Clinic in either Lebanon or Manchester.


Information on the Dartmouth-Hitchcock Medical Center (DHMC) website:

  • is not provided as medical advice
  • does not establish a doctor-patient or other relationship
  • is not intended nor should be assumed to guarantee a specific result

Our goals are to provide people with meaningful information to make informed decisions about their health and health care.

DHMC and its affiliated component organizations aspire to deliver consistent high quality medical care to all patients and to continually improve its quality of care as evolving technology and medical knowledge permits.

Please call 911 in the case of any medical emergency.

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