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 cy