Sweat Test - Test Overview

A sweat test measures the amount of salt chemicals (sodium and chloride) in sweat. It is done to help diagnose cystic fibrosis. Normally, sweat on the skin surface contains very little sodium and chloride. People with cystic fibrosis have 2 to 5 times the normal amount of sodium and chloride in their sweat.

During the sweat test, medicine that causes a person to sweat is applied to the skin (usually on the arm or thigh). The sweat is then collected on a paper or a gauze pad, and the amount of salt chemicals in the paper or gauze is measured in a lab. Generally, chloride (sweat chloride) is measured. See a picture of a sweat test.

A sweat test is done on any baby suspected of having cystic fibrosis. An initial test may be done as early as 48 hours of age. But a sweat test done during the first month of life may need to be repeated. Younger babies may not produce enough sweat to give reliable test results. Also, younger babies may naturally have lower sweat chloride levels than older babies and children with cystic fibrosis.