Sweat electrolytes is a test that measures the level of chloride in sweat. Sweat chloride test is the standard test used to diagnose cystic fibrosis.
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 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.
How to Prepare for the Test
No special steps are needed before this test.
Normal results include:
- 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.
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 United States, newborn screening programs test for cystic fibrosis. The sweat test is used to confirm these results.
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, Green DM, Voynow JA. Cystic fibrosis. In: Kliegman RM, Stanton BF, St. Geme JW, Schor NF, eds. Nelson Textbook of Pediatrics. 20th ed. Philadelphia, PA: Elsevier; 2016:chap 403.
Farrell PM, White TB, Ren CL, et al. Diagnosis of cystic fibrosis: consensus guidelines from the Cystic Fibrosis Foundation. J Pediatr. 2017;181S:S4-S15.e1. PMID: 28129811