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
- 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
- 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).
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
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