A sweat test measures the amount of salt chemicals (sodium and
chloride) in sweat. It is done to help diagnose Reference cystic
fibrosis Opens New Window. 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 Reference sweat test Opens New
Window Reference Opens New Window. A sweat test is done on any
person 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 ma