Sweat Chloride Test

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KEY POINTS

• The sweat chloride test measures the amount of a chemical called chloride in your child’s sweat. This test is done to diagnose cystic fibrosis.
• A small amount of sweat is collected from your child’s skin and sent to a lab.
• Talk to your healthcare provider about what the test results mean and ask any questions you have.

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What is the sweat chloride test?

This test measures the amount of chloride in your child’s sweat. Chloride is one of several chemicals in the body called electrolytes. Electrolytes help control the amount of fluid in your child’s body and the way the muscles, nerves, and organs work. Your child needs the right balance of chloride and other electrolytes in the body to stay healthy. The balance of electrolytes in the body can be affected by food, medicines, drinking too much or too little water, or problems with your child’s lungs, kidneys, and other organs.

Why is this test done?

This test is done to diagnose cystic fibrosis (CF). CF is a disease that causes the body to make thick, sticky mucus. The thick mucus blocks airways, damages the lungs, and makes it hard to breathe. People with CF have more chloride (salt) in their sweat than someone who does not have CF.

This test is done when an infant has a positive newborn screening test for CF or if a person has signs or symptoms that might be due to CF.

How do I prepare my child for this test?

You and your child should avoid applying large amounts of creams or lotions on the skin for 24 hours before the test. Your child can take any regular medicines before the test. Talk to your child’s healthcare provider if you have any questions.

How is the test done?

To do the sweat test, clear odorless chemical that causes sweating is put on a small part of the arm. A wire is put on that spot. A weak electrical current causes the area to sweat. The whole area is covered in plastic wrap to promote sweating and allow collection of the sweat. Enough sweat is usually collected in 30 minutes and sent to the lab for testing. This test does not hurt.

Ask your child’s healthcare provider how and when you will get your child’s test results.

What does the test result mean?

A child with CF has more chloride (salt) in their sweat than those who do not have CF. A positive sweat chloride test means that it was high and it is likely that your child has CF.

What if my child’s test result is not normal?

Test results are only one part of a larger picture that takes into account your child’s medical history and current health. Sometimes a test needs to be repeated to check the first result. Talk to your healthcare provider about the result and ask questions such as:

• If your child needs more tests
• What kind of treatment your child might need
• What lifestyle, diet, or other changes your child might need to make