Cystic Fibrosis: When Your Child Needs a Sweat Test

Adult Health Library

A sweat test confirms if your child has cystic fibrosis. A sweat test is an easy, simple, and accurate test. It's 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 normal. They won’t affect test results.
Don't use lotion, cream, 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.
In an age-appropriate way, let your child know what will happen.

During the test

Woman watching boy play with blocks. Boy has gauze wrapped around both forearms.

Your child can play while the sweat test is being done.

This is a painless test. It doesn't use 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's painless. But it may cause mild tingling or warmth. The electrode stays 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 is to collect 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. Ask your child’s healthcare provider how soon you will get the test result. In rare cases, a child doesn’t make enough sweat or the test is not clear. The test can be repeated. Or your child can have other tests to confirm a diagnosis.