URL of this page: https://medlineplus.gov/lab-tests/sweat-test-for-cystic-fibrosis/

Sweat Test for Cystic Fibrosis

What is a sweat test?

A sweat test measures the amount of chloride, a part of salt, in Sweat. It is used to diagnose cystic fibrosis (CF). People with CF have a high level of chloride in their sweat.

CF is a disease that causes mucus build-up in the lungs and other organs. It damages the lungs and makes it hard to breathe. It can also lead to frequent infections and malnutrition. CF is an inherited disease, which means it is passed down from your parents, through genes.

Genes are parts of DNA that carry information that determine your unique traits, such as height and eye color. Genes are also responsible for certain health problems. To have cystic fibrosis, you must have a CF gene from both your mother and your father. If only one parent has the gene, you will not get the disease.

Other names: sweat chloride test, cystic fibrosis sweat test, sweat electrolytes

What is it used for?

A sweat test is used to diagnose cystic fibrosis.

Why do I need a sweat test?

A sweat test can diagnose cystic fibrosis (CF) in people of all ages, but it's usually done on babies. In the United States, new babies usually get a series of tests called a newborn screening. The tests check for a variety of conditions including CF. 

Your baby may need a sweat test if a newborn screening shows that he or she might have CF. The sweat test can confirm or rule out the diagnosis. Most sweat tests are done when babies are 2 to 4 weeks old. 

An older child or adult who has never been tested for CF may need a cystic fibrosis sweat test if someone in the family has the disease and/or has symptoms of CF. These include:

  • Salty-tasting skin
  • Frequent coughing
  • Frequent lung infections, such as pneumonia and bronchitis
  • Trouble breathing
  • Failure to gain weight, even with a good appetite
  • Greasy, bulky stools
  • In newborns, no stools made right after birth

What happens during a sweat test?

Your health care provider will need to collect a sample of sweat for testing. The entire procedure will take about an hour and will probably include the following steps:

  • A health care provider will put pilocarpine, a medicine that causes sweating, on a small area of the forearm.
  • Your provider will place an electrode on this area.
  • A weak current will be sent through the electrode. This current makes the medicine seep into the skin. This may cause a little tingling or warmth.
  • After removing the electrode, your provider will tape a piece of filter paper or gauze on the forearm to collect the sweat.
  • Sweat will be collected for 30 minutes.
  • The collected sweat will be sent to a lab for testing.

Will I need to do anything to prepare for the test?

You don't need any special preparations for a sweat test, but you should avoid applying any creams or lotions to the skin for 24 hours before the procedure.

Are there any risks to the test?

There is no known risk to a sweat test. Your child may have a tingling or tickling sensation from the electric current, but should not feel any pain.

What do the results mean?

If the results show a high level of chloride, there is a good chance your child has cystic fibrosis. Your health care provider will probably order another sweat test and/or other tests to confirm or rule out a diagnosis. If you have questions about your child's results, talk to your health care provider.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about a sweat test?

While there is no cure for cystic fibrosis (CF), there are treatments available that help reduce symptoms and improve quality of life. If your child was diagnosed with CF, talk with your health care provider about strategies and treatments to help manage the disease.

References

  1. American Lung Association [Internet]. Chicago: American Lung Association; c2018. Diagnosing and Treating Cystic Fibrosis; [cited 2018 Mar 18]; [about 4 screens]. Available from: http://www.lung.org/lung-health-and-diseases/lung-disease-lookup/cystic-fibrosis/diagnosing-and-treating-cf.html
  2. Cystic Fibrosis Foundation [Internet]. Bethesda (MD): Cystic Fibrosis Foundation; About Cystic Fibrosis; [cited 2018 Mar 18]; [about 2 screens]. Available from: https://www.cff.org/What-is-CF/About-Cystic-Fibrosis
  3. Cystic Fibrosis Foundation [Internet]. Bethesda (MD): Cystic Fibrosis Foundation; Sweat Test; [cited 2018 Mar 18]; [about 3 screens]. Available from: https://www.cff.org/What-is-CF/Testing/Sweat-Test
  4. Hinkle J, Cheever K. Brunner & Suddarth’s Handbook of Laboratory and Diagnostic Tests. 2nd Ed, Kindle. Philadelphia: Wolters Kluwer Health, Lippincott Williams & Wilkins; c2014. Sweat Test; p. 473-74.
  5. Johns Hopkins Medicine [Internet]. Baltimore: The Johns Hopkins University; Health Library: Cystic Fibrosis; [cited 2018 Mar 18]; [about 3 screens]. Available from: https://www.hopkinsmedicine.org/healthlibrary/conditions/adult/respiratory_disorders/cystic_fibrosis_85,p01306
  6. Lab Tests Online [Internet]. Washington D.C.: American Association for Clinical Chemistry; c2001–2018. Cystic Fibrosis; [updated 2017 Oct 10; cited 2018 Mar 18]; [about 2 screens]. Available from: https://labtestsonline.org/conditions/cystic-fibrosis
  7. Lab Tests Online [Internet]. Washington D.C.: American Association for Clinical Chemistry; c2001–2018. Newborn Screening; [updated 2018 Mar 18; cited 2018 Mar 18]; [about 2 screens]. Available from: https://labtestsonline.org/screenings/newborns
  8. Lab Tests Online [Internet]. Washington D.C.: American Association for Clinical Chemistry; c2001–2018. Sweat Chloride Test; [updated 2018 Mar 18; cited 2018 Mar 18]; [about 2 screens]. Available from: https://labtestsonline.org/tests/sweat-chloride-test
  9. Merck Manual Consumer Version [Internet]. Kenilworth (NJ): Merck & Co. Inc.; c2018. Cystic Fibrosis (CF); [cited 2018 Mar 18]; [about 2 screens]. Available from: https://www.merckmanuals.com/home/children-s-health-issues/cystic-fibrosis-cf/cystic-fibrosis-cf
  10. National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Cystic Fibrosis; [cited 2018 Mar 18]; [about 3 screens]. Available from: https://www.nhlbi.nih.gov/health-topics/cystic-fibrosis
  11. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2018. Health Encyclopedia: Cystic Fibrosis Sweat Test; [cited 2018 Mar 18]; [about 2 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid;=cystic_fibrosis_sweat
  12. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2018. Health Information: Health Facts for You: Pediatric Sweat Test; [updated 2017 May 11; cited 2018 Mar 18]; [about 3 screens]. Available from: https://www.uwhealth.org/healthfacts/parenting/5634.html
  13. UW Health: American Family Children’s Hospital [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2018. Kids Health: What is Cystic Fibrosis (CF)?; [cited 2020 May 4]; [about 3 screens]. Available from: https://www.uwhealthkids.org/cf-center/what-is-cystic-fibrosis-cf/34311
  14. UW Health: American Family Children’s Hospital [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2018. Kids Health: Cystic Fibrosis (CF) Newborn Screening: Sweat Testing; [cited 2020 May 4]; [about 4 screens]. Available from: https://www.uwhealthkids.org/cf-center/cystic-fibrosis-cf-newborn-screening-sweat-testing/34314

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.