Cystic Fibrosis: When Your Child Needs a Sweat Test

Woman watching boy play with blocks. Boy has gauze wrapped around both forearms.A sweat test confirms whether or not your child has cystic fibrosis. A sweat test is an easy, simple, and accurate test. It is safe for a child of any age. Its purpose is to make the skin sweat enough to collect salt. A high level of salt in the sweat is common in people with cystic fibrosis.

Before the test

  • Give your child any regular medicines as usual. They won’t affect test results.

  • Avoid using lotion or soap on your child’s arms or legs for 24 hours before the test.

  • Bring something to help your child stay warm during the test. You can bring a blanket, sweater, or jacket.

During the test

This is a painless test that uses no needles. It takes about 60 minutes to complete. Here’s what you can expect:

  • A technician applies an odorless, colorless chemical to a small area on your child’s arm or leg.

  • The technician then attaches an electrode to this area. The electrode produces a weak electrical current. This causes sweating. It is painless, but may cause mild tingling or warmth. The electrode remains in place for about 5 minutes.

  • The technician removes the electrode, then cleans and dries the area.

  • Next, the technician applies filter paper, gauze, or a plastic coil to your child’s skin. This collects sweat for about 30 minutes. During this time, your child can move around, eat, play, or relax.

  • The collection device is removed and sent to a lab for analysis.

After the test

You and your child can go home after the test. Your child’s doctor will receive the test result within a day or two. In rare cases, a child doesn’t produce enough sweat or the test is not clear. The test can be repeated. Or, your child can have other tests to confirm a diagnosis.

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