Sweat test for cystic fibrosis: How it works and who needs it

Oct 25, 2023

The sweat test involves measuring the amount of chloride in sweat. Doctors may use the sweat test to help diagnose cystic fibrosis, as cystic fibrosis causes higher amounts of chloride in sweat.

The sweat test can be useful for diagnosing cystic fibrosis in babies, children, and adults. A doctor may order a sweat test if a person has symptoms of cystic fibrosis or as part of a newborn screening test.

Read on to learn more about the sweat test. This article discusses how it can help diagnose cystic fibrosis, what the test involves, who might need it, and more.

The sweat test is a test that measures the amount of chloride a person has in their sweat.

Each person's body contains two copies of the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The genes produce the CFTR protein.

When a person has cystic fibrosis, the CFTR protein does not work properly. This can cause chloride, which is a component of salt, to become trapped in the cells.

This can result in more chloride in a person's sweat. If the sweat test detects higher chloride levels, this can indicate cystic fibrosis.

Learn more about diagnosing cystic fibrosis.

The sweat test involves placing pads soaked in the chemical pilocarpine on the lower arm or leg. This helps to stimulate sweat production.

A small electrical current will then be passed through the pads for about 5 minutes. This helps the chemical to seep into the skin. It does not cause any pain.

Afterward, the sweat will be collected with a piece of gauze, filter paper, or a small plastic coil. This will typically last for about 30 minutes.

A doctor may order a sweat test if a child or adult has symptoms of cystic fibrosis. They may also recommend the test if a person has a family history of cystic fibrosis.

The sweat test may also be carried out as part of newborn screening tests. Babies in the United States are screened for a variety of conditions after birth, including cystic fibrosis.

If the heel prick test indicates that the baby might have cystic fibrosis, a doctor may order a sweat test to confirm the diagnosis.

Learn about cystic fibrosis and genetics.

A doctor may recommend not applying any creams or lotions to the arms or legs in the 24 hours before the sweat test.

A person will typically not need to do anything else to prepare for a sweat test.

If the sweat test measures a low level of chloride salts, then this typically suggests that the person does not have cystic fibrosis.

If the sweat test measures a high level of chloride, then this may indicate cystic fibrosis. A doctor may then order blood tests to confirm the diagnosis.

In some cases, the results may be inconclusive. If this is the case, a person may need to take another sweat test.

A sweat test is a test that can help with diagnosing cystic fibrosis. It measures the levels of chloride a person has in their sweat.

The test involves placing pilocarpine-soaked pads on the skin and passing a weak electrical current through the pad. Afterward, the sweat will be collected to test the level of chloride.

A person may need this test if they have symptoms or a family history of cystic fibrosis. It may also be necessary if a baby's heel prick test suggests that cystic fibrosis might be possible.

A high level of chloride can indicate cystic fibrosis. Blood tests can then help to confirm the diagnosis.