Sweat Test

Cystic Fibrosis Sweat Test

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 may be 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. Another testing method collects the sweat into a coil (macroduct technique).
• 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.
• 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.

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Author:	Debby Golonka, MPH	Last Updated: June 26, 2007
Medical Review:	Michael J. Sexton, MD - Pediatrics Susanna McColley, MD - Pediatric Pulmonology
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