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    Sweat electrolytes test

    Sweat test; Sweat chloride; Iontophoretic sweat test

    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.

    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.

    Normal 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.

    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.

    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).

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          Tests for Sweat electrolytes test

          Review Date: 5/1/2011

          Reviewed By: Denis Hadjiliadis, MD, Assistant Professor of Medicine, Division of Pulmonary, Allergy and Critical Care, University of Pennsylvania, Philadelphia, PA. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

          The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.
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