How It Is Done
The sweat test is usually done on a baby's arm or thigh. On an older child or adult, the test is usually done on the inside of the forearm. Sweat is usually collected and analyzed from two different sites.
- The skin is washed and dried, then two small gauze pads are placed on the skin. One pad is soaked with a medicine that makes the skin sweat, called pilocarpine. The other pad is soaked with salt water.
- Other pads called electrodes are placed over the gauze pads. The electrodes are hooked up to an instrument that produces a mild electric current, which pushes the medicine into the skin.
- After 5 to 10 minutes, the gauze pads and electrodes are removed, and the skin is cleaned with water and then dried. The skin will look red in the area under the pad that contained the medicine.
- A dry gauze pad, paper collection pad, or special tubing is taped to the red patch of skin. This pad is covered with plastic or wax to prevent fluid loss (evaporation).
- The new pad will soak up the sweat for up to 30 minutes, then it is removed and placed in a sealed bottle. It is then weighed to measure how much sweat the skin produced, and it is checked to find out how much salt chemical (sodium and/or chloride) the sweat contains. Another testing method collects the sweat into a coil (macroduct technique).
- After the collection pad is removed, the skin is washed and dried again. The test site may look red and continue to sweat for several hours after the test.
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.