A sweat test measures the amount of salt chemicals (sodium and chloride) in sweat. It is done to help diagnose cystic fibrosis. Normally, sweat on the skin surface contains very little sodium and chloride. People with cystic fibrosis have 2 to 5 times the normal amount of sodium and chloride in their sweat.
During the sweat test, medicine that causes a person to sweat is applied to the skin (usually on the arm or thigh). The sweat is then collected on a paper or a gauze pad, and the amount of salt chemicals in the paper or gauze is measured in a lab. Generally, chloride (sweat chloride) is measured. See a picture of a sweat test.
A sweat test is done on any person suspected of having cystic fibrosis. An initial test may be done as early as 48 hours of age. But a sweat test done during the first month of life may need to be repeated. Younger babies may not produce enough sweat to give reliable test results. Also, younger babies may naturally have lower sweat chloride levels than older babies and children with cystic fibrosis.
Why It Is Done
The sweat test is done to help diagnose cystic fibrosis. It also may be used to test people with a family history of cystic fibrosis and for anyone with symptoms of cystic fibrosis.
How To Prepare
No special preparation is needed before having this test. Your child may eat, drink, and exercise normally before the test. If your child takes any medicines, he or she may take them on the usual schedule.
You may help with the test and stay with your child during the test. If you can't stay, you may want to ask a family member or friend to stay with your child. Bring your child's favorite book or toy to help pass the time while the test is done. See if your child might be able to watch a movie during the test.
Talk with your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?). For more information, see the topic Pediatric Preparation for Medical Tests.
How It Is Done
The sweat test is usually done on a baby's right arm or thigh. On an older child or adult, the test is usually done on the inside of the right forearm. Sweat is usually collected and analyzed from two different sites.
The sweat test usually takes 45 minutes to 1 hour.
How It Feels
This test does not cause pain. Some children feel a light tingling or tickling when the electric current is applied to the skin. If the gauze pads are not properly placed, the electric current may produce a burning sensation.
There is very little risk of complications from this test. But the test should always be done on an arm or leg (not the chest) to prevent the possibility of electric shock.
The electric current may cause skin redness and excess sweating for a short time after the test is done. In rare cases, the current may make the skin look slightly sunburned.
A sweat test measures the amount of salt chemicals (sodium and chloride) in sweat. Generally, chloride (sweat chloride) is measured.
Results are usually available in 1 or 2 days. Normal results vary from lab to lab.
Many conditions can change sodium and chloride levels. Your doctor will discuss any significant abnormal results with you in relation to your symptoms and past health.
The test results do not show how severe the cystic fibrosis is. The test only shows if a person could have the disease.
Abnormal (high) values
What Affects the Test
Reasons your child may not be able to have the test or why the results may not be helpful include:
What To Think About
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