Sweat Test

A sweat test may be ordered if a doctor thinks a child might have cystic fibrosis (CF). Cystic fibrosis is an inherited disease that causes sweat glands and other glands, especially those in the pancreas and the air passages of the lungs, to produce abnormally thick, clogging mucus. This clogging causes many problems for the patient, especially in the lungs. Though there are some promising new developments, there currently is no cure for CF, so early diagnosis and proper treatment are essential to improving the patient's quality of life and life span.

How Is a Sweat Test Done?

A device for collecting sweat is placed on the child's skin, and a colorless, odorless chemical is applied that causes the child to sweat. Assuming enough sweat is collected (sometimes collection can be difficult, especially in babies), the sweat is analyzed for sodium and chloride, components also found in blood, sweat, and tears.

The diagnosis of CF isn't made on the basis of just one test -- it requires two (or more) abnormal sweat tests. When the level of chloride is elevated beyond a certain point in two consecutive tests, the child may be diagnosed with CF. However, a number of other conditions can also show elevated sweat electrolytes.

How Long Does a Sweat Test Take?

The sweat collection takes about 30 minutes to 1 hour. If not enough sweat is collected, the test may need to be repeated.

After a child is diagnosed with CF, further genetic testing can help doctors determine the specific type of the disease the child has.