Sweat electrolytes is a test that measures the level of chloride in sweat. Although genetic tests have become important methods for diagnosing cystic fibrosis in children, the sweat chloride test is still the standard.
Sweat test; Sweat chloride; Iontophoretic sweat test
How the test is performed
In the first part of the test, a colorless, odorless chemical that causes sweating is applied to a small area on an arm or leg. An electrode is then attached to the arm or leg. A weak electrical current is sent to the area to stimulate sweating.
People may feel a tingling in the area, or a feeling of warmth. This part of the procedure lasts for about 5 minutes.
The next part of the test involves cleaning the stimulated area and collecting the sweat on a piece of filter paper or gauze, or in a plastic coil. After 30 minutes, the collected sweat is sent to a hospital laboratory to be tested. The entire collection procedure takes about 1 hour.
How to prepare for the test
No special preparation is needed. Make sure the test is performed at a cystic fibrosis testing center.
How the test will feel
Though the test is not painful, some people describe a tingling sensation at the site of the electrode. In smaller children or infants, the sensation can cause irritability or discomfort.
Why the test is performed
Sweat testing is the standard method for diagnosing cystic fibrosis. People with cystic fibrosis have higher amounts of sodium and chloride in their sweat, which the test can detect.
Some people are tested because of symptoms such as poor nutrition, repeated sinus or respiratory infections, foul-smelling stools, or infertility (in men). In the U.S., newborn screening programs test for cystic fibrosis, and the sweat test is used to confirm these results.
- A sweat chloride test result of less than or equal to 39 mEq/L in an infant over 6 months old probably means cystic fibrosis is not present.
- A result between 40 - 59 mEq/L does not give a clear diagnosis. Further testing is needed.
- If the result is 60 mEq/L or greater, cystic fibrosis is present.
Note: mEq/L = milliequivalent per liter
Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
Some conditions, such as dehydration or swelling (edema) can affect the test results.
What abnormal results mean
An abnormal test may mean that the child has cystic fibrosis.
Borowitz D, Robinson KA, Rosenfeld M, et al. Cystic Fibrosis Foundation evidence-based guidelines for management of infants with cystic fibrosis. J Pediatr. 2009;155(6 Suppl):S73-S93.
Boat TF, Acton JD. Cystic fibrosis. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 400.
Farrell PM, Rosenstein BJ, White TB, et al. Guidelines for diagnosis of cystic fibrosis in newborns through older adults: Cystic fibrosis consensus report. Journal of Pediatrics. Aug 2008;153(2).