What is a sweat test?

A sweat test is a medical test used to measure the amount of chloride excreted from the body along with sweat. The amount is measured over a specific period of time and is used to determine if a child has or may have cystic fibrosis. This disease causes victims to produce higher concentrations of chloride and sodium in their sweat.

Cystic fibrosis can cause children to be stunted, have digestive problems, and have a variety of serious breathing problems. Cystic fibrosis was a death sentence in the first half of the 20th century, and affected children generally did not live beyond their first year. Improved treatments mean that people diagnosed with cystic fibrosis in the 21st century can expect to live into adulthood, although the disease requires ongoing treatment.

Excess sodium produced in sweat, as much as two to five times higher than normal, is often the first indicator that there is a problem. Parents often tell the child's doctor that the child tastes salty. This observation is usually enough to cause the doctor to order a sweat test. Such children will often have a positive test, resulting in a diagnosis of cystic fibrosis.

A sweat test helps doctors diagnose this condition in children up to 2 days of age, although babies this age may not produce enough sweat for an accurate reading. The test does not require any special preparation, and children being tested can go about their normal activities until the time of the test. Once in the office or lab, a sweat test will take about an hour.

The procedure for the sweat test is quite simple. A chemical that causes the child to sweat is applied to his arm. A weak, painless electrical current is then used to further trigger sweating in the test area. The sweat is then collected and analyzed for elevated amounts of chlorine and sodium.

Although a sweat test is often used to confirm a diagnosis of cystic fibrosis, it may not be conclusive. In these cases, the doctor may order additional tests to confirm the presence or absence of the disease. Deoxyribonucleic acid (DNA) is sometimes collected from saliva or blood and tested for genetic indicators of cystic fibrosis. No matter how the diagnosis is made, treatment for this disease begins as soon as possible. Patient care is a lifelong process.

Go up