Sweat Test

People with cystic fibrosis have an abnormal amount of salt in their sweat. The sweat test measures the amount of that salt and helps a doctor arrive at a diagnosis.

How is the sweat test done?

The sweat test is painless and does not require needles.

  1. A small amount of a solution that causes sweating will be put on your child's forearm.
  2. Small electrodes are placed over the solution. A very small (and safe) electrical current passes through the electrodes, pushing 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."
  3. After five minutes the electrodes are removed and the area is covered with gauze to absorb the sweat. The gauze stays in place for 30 minutes and is then removed and sent to the lab.
  4. 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 usually come back in about two hours.

Test results

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 the child has cystic fibrosis. That child will be seen on a regular basis in the Cystic Fibrosis Center in either Lebanon or Manchester, NH.