Sweat electrolytes test

  • Definition
    • Sweat electrolytes is a test that measures the level of chloride in sweat. Sweat chloride test is the standard test used to diagnose cystic fiborsis.

  • Alternative Names
    • Sweat test; Sweat chloride; Iontophoretic sweat test

  • How the Test is Performed
    • 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 spot. 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.

      Next, the stimulated area is cleaned and the sweat is collected on a piece of filter paper or gauze, or in a plastic coil.

      After 30 minutes, the collected sweat is sent to a hospital lab to be tested. The collection takes about 1 hour.

  • How to Prepare for the Test
    • No special steps are needed before this test.

  • How the Test will Feel
    • The test is not painful. Some people have a tingling feeling at the site of the electrode. This feeling may cause discomfort in small children.

  • 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 that are detected by the test.

      Some people are tested because of symptoms they are having. In the U.S., newborn screening programs test for cystic fibrosis. The sweat test is used to confirm these results.

  • Normal Results
      • A sweat chloride test result of less than or equal to 39 mmol/L in an infant over 6 months old probably means cystic fibrosis is very unlikely.
      • A result between 40 to 59 mmol/L does not give a clear diagnosis. Further testing is needed.
      • If the result is 60 mmol/L or greater, cystic fibrosis is present.

      Note: mmol/L = millimole per liter

      Normal value ranges may vary slightly among different laboratories. Talk to your health care provider 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.

  • References
    • 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. PMID: 19914445

      Egan M. Cystic fibrosis. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 395.

      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). PMID: 18639722