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Sweat Test for Cystic Fibrosis

What is a sweat test? A sweat test measures the amount of chloride in your sweat . Chloride is a type of electrolyte . Electrolytes are electrically charged minerals  that help control the amount of fluids and the balance of acids and bases (pH balance) in yo

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This guide cannot diagnose a condition or recommend a personal treatment plan. Discuss medical questions with a qualified professional.

What is a sweat test?

A sweat test measures the amount of chloride in your sweat . Chloride is a type of electrolyte . Electrolytes are electrically charged minerals  that help control the amount of fluids and the balance of acids and bases (pH balance) in your body. Chloride and sodium form the salt found in your sweat.

Normally, chloride moves in and out of your cells through a protein called the cystic fibrosis membrane conductance regulator (CFTR). This protein can be found in the organs that make sweat and mucus, such as your lungs, sweat glands, and intestines. Mucus is the slippery substance that protects the linings of your airways, digestive tract, and other organs and tissues.

If the CFTR protein isn't working as it should, however, chloride can't as easily move in and out of the cells in your mucus/sweat-producing organs. This condition is called cystic fibrosis  (CF). If you have CF, you will also have much more chloride in your sweat.

With CF, chloride builds up in your cells, causing your mucus to become thick and sticky. When this happens, mucus can build up in your organs. This can not only make it hard to breathe but can lead to frequent lung infections  and organ damage.

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 (CF).

CF is an inherited disease  that can affect people of all ages. To have cystic fibrosis, you must inherit a changed CFTR gene from both your parents. (Changes in genes are also called variants or mutations.) If you inherit one changed gene, you won't have the disease, but you will be a carrier. Being a carrier means that if you have children with someone who also has changes in one or both of their CFTR genes, your children could inherit two changed genes and have CF.

CF most commonly affects the lungs. However, it can also cause malnutrition  because the disease may reduce your body's ability to absorb nutrients from food.

Why do I need a sweat test?

A sweat test may be ordered if your health care provider suspects you or your child has cystic fibrosis (CF). It's most commonly ordered for newborns. In the United States, babies have newborn screening  tests to check for a variety of conditions, including CF. If a screening test shows that your baby may have CF, a sweat test will be needed to make a diagnosis.

It's best if the test is done when your baby is between 10 days and 4 weeks old. Starting treatment as soon as possible can delay or prevent health problems from CF.

A provider may also order a cystic fibrosis sweat test for a child or adult if they have symptoms of CF or if someone in the family has CF. Most people with CF have symptoms, but some people don't. In milder cases, symptoms may not show up until adulthood. The symptoms of CF depend on which organs are affected and may include:

  • A wheeze or cough that may produce mucus or blood.
  • Clubbing of fingers and toes , which means that your fingernails and toenails are wide and rounded like the back of a spoon. This is usually due to a low level of oxygen in your blood that happens if your lungs aren't working well. The lack of oxygen may also cause changes in your nails.
  • Fever , which may include night sweats (heavy sweating during sleep).
  • Digestive symptoms , such as severe abdominal (belly) pain, chronic (long-lasting) diarrhea , or constipation . Children may also have oily or loose stools.
  • Being underweight .
  • Muscle and joint pain.
  • Delayed growth.
  • Delayed puberty .
  • Salty skin and saltier than normal sweat.
  • Sinus infections .
  • Infertility , especially in men.

If your provider suspects CF, it's important to get tested. There is no cure for CF, but treatment can help you and/or your child live a longer, healthier life.

What happens during a sweat test?

To do a sweat test, a health care professional will collect a sample of sweat from you or your child. This takes about an hour and usually includes the following steps:

  • Your provider will wash and pat dry a small area of the forearm or leg.
  • To cause sweating, an odorless chemical (pilocarpine) will be applied to the small area of the forearm or leg. An electrode will be taped over the area.
  • A weak electrical current will be sent through the electrode to make the chemical seep into the skin. This may cause a little tingling or warmth.
  • After about 5 minutes, the electrode will be removed. The health care professional will collect the sweat by taping a piece of filter paper or gauze on the area or by using a small plastic coil.
  • Sweat will be collected for 30 minutes.
  • The sweat sample will be sent to a lab for testing.

Some babies may not produce enough sweat for the test on the first try. If this happens, the test will usually be repeated on another day.

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 test.

Are there any risks to the test?

There is no known risk to a sweat test. The electrode may cause a tingling or tickling sensation from the electric current, but this is not painful.

What do the results mean?

Chloride in sweat is measured in mmol/L (millimoles of chloride per liter of sweat):

  • A chloride level of 60 or greater means that you or your child most likely has cystic fibrosis. To confirm the diagnosis, your provider may have you repeat the test or order a CF genetic test.
  • A chloride level of 30 to 59 means that more testing is needed because the test result is unclear, and CF is possible. Your provider may order another sweat test or a different type of test, such as genetic testing .
  • A chloride level less than 29 is normal. This means that you or your child is unlikely to have CF. But a normal test result doesn't rule out CF. Certain people with CF have normal sweat test results. If you or your child have symptoms of CF or if your baby had a newborn screening test that showed possible CF, your provider may order more tests.

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

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

In rare cases, conditions other than CF may result in high chloride levels on a sweat test. These conditions include hypothyroidism , nephrogenic diabetes insipidus , and Addison disease .

References

  • American Lung Association [Internet]. Chicago: American Lung Association; c2025. Diagnosing and Treating Cystic Fibrosis; [updated 2024 Oct 30; cited 2025 May 30]; [about 3 screens]. Available from: https://www.lung.org/lung-health-diseases/lung-disease-lookup/cystic-fibrosis/symptoms-diagnosis
  • Centers for Disease Control and Prevention [Internet]. Atlanta: U.S. Department of Health and Human Services; About Cystic Fibrosis; [reviewed 2024 May 15; cited 2025 May 30]; [about 2 screens]. Available from: https://www.cdc.gov/cystic-fibrosis/about/index.html
  • Cleveland Clinic: Health Library: Diagnostics & Testing [Internet]. Cleveland (OH): Cleveland Clinic; c2025. Sweat Test for Cystic Fibrosis (CF); [reviewed 2019 Feb 14; cited 2025 May 30]; [about 7 screens]. Available from: https://my.clevelandclinic.org/health/diagnostics/17856-sweat-test-for-cystic-fibrosis-cf
  • Cystic Fibrosis Foundation [Internet]. Bethesda (MD): Cystic Fibrosis Foundation; About Cystic Fibrosis; [cited 2025 May 30]; [about 15 screens]. Available from: https://www.cff.org/intro-cf/about-cystic-fibrosis
  • Cystic Fibrosis Foundation [Internet]. Bethesda (MD): Cystic Fibrosis Foundation; Sweat Test; [cited 2025 May 30]; [about 7 screens]. Available from: https://www.cff.org/intro-cf/sweat-test
  • Johns Hopkins Medicine [Internet]. Baltimore: The Johns Hopkins University, The Johns Hopkins Hospital and Johns Hopkins Health System; c2025. Health Library: Cystic Fibrosis; [cited 2025 May 30]; [about 9 screens]. Available from: https://www.hopkinsmedicine.org/health/conditions-and-diseases/cystic-fibrosis
  • Merck Manual Consumer Version [Internet]. Kenilworth (NJ): Merck & Co. Inc.; c2025. Cystic Fibrosis (CF); [updated 2025 Apr; cited 2025 May 30]; [about 15 screens]. Available from: https://www.merckmanuals.com/home/children-s-health-issues/cystic-fibrosis/cystic-fibrosis-cf
  • National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Cystic Fibrosis: What Is Cystic Fibrosis?; [updated 2024 Nov 15; cited 2025 May 30]; [about 4 screens]. Available from: https://www.nhlbi.nih.gov/health/cystic-fibrosis
  • Nemours KidsHealth [Internet]. Jacksonville (FL): The Nemours Foundation; c1995-2025. Cystic Fibrosis; [reviewed 2020 Jul; cited 2025 May 30]; [about 6 screens]. Available from: https://kidshealth.org/en/parents/cf.html
  • Nemours KidsHealth [Internet]. Jacksonville (FL): The Nemours Foundation; c1995-2025. Cystic Fibrosis (CF) Chloride Sweat Test; [reviewed 2021 Jan; cited 2025 May 30]; [about 5 screens]. Available from: https://kidshealth.org/en/parents/sweat-test.html
  • Schmidt H, Sharma G. Sweat Testing. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. [Updated 2025 Feb 17; cited 2025 May 30]; [about 7 screens]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK547728/
  • Testing.com [Internet]. Seattle (WA).: OneCare Media; c2025. Cystic Fibrosis (CF) Gene Mutations Testing; [modified 2021 Nov 9; cited 2025 May 30]; [about 14 screens]. Available from: https://www.testing.com/tests/cystic-fibrosis-cf-gene-mutations-testing/
  • Testing.com [Internet]. Seattle (WA).: OneCare Media; c2025. Sweat Chloride Test; [modified 2021 Jan 27; cited 2025 May 30]; [about 12 screens]. Available from: https://www.testing.com/tests/sweat-chloride-test/

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.

Connected reading

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Related questions

01What you can do

You might want to take a friend or family member with you to the appointment to help you remember information. Before your appointment, make a list of: Symptoms and when they started. Include anything that makes symptoms worse or better. All medicines, vitamins, herbs and supplements that you or your child take. Include the doses. Family history, such as whether anyone in your family has cystic fibrosis. Treatment you or your child have had for CF, if any. Include what the treatment was and if it helped. Any other medical conditions and their treatments. Questions to ask your healthcare professional. Questions to ask may include: What is likely causing these symptoms? What kinds of tests are needed? What treatment do you recommend? I or my child have other health conditions. How will cystic fibrosis affect them? Are there any limits needed? Feel free to ask other questions during your appointment.

Source: www.mayoclinic.org ↗
02How Does Alyftrek Work?

Alyftrek is a type of medicine called a CFTR modulator. Alyftrek is designed to help make the broken CFTR protein in people with cystic fibrosis work better. Since different genetic mutations can cause different types of problems with the protein, the medicines available today only work for people with certain mutations. Alyftrek is approved for people who have at least one F508del mutation or another responsive mutation in the CFTR gene. Alyftrek contains three active ingredients (vanzacaftor, tezacaftor, and deutivacaftor) that work together to help the CFTR protein work better. Vanzacaftor and tezacaftor help the CFTR protein fold correctly and move to the cell surface, while deutivacaftor increases CFTR activity to lower the buildup of mucus. By helping CFTR work better, Alyftrek helps thin mucus in the lungs and other organs, making it easier to clear and reducing complications of cystic fibrosis.

Source: www.webmd.com ↗
03What Is Cystic Fibrosis?

Cystic fibrosis (CF) is a genetic disorder, which means you get it from your parents at birth. It affects your lungs, pancreas, and other organs. CF changes the way chloride (salt) moves through the cells of your body. This causes the mucus (which should be thin and slippery) in various organs to become thick and sticky. Over time, this thick mucus builds up inside your airways, making it hard to breathe. The mucus traps germs and leads to infections and inflammation. It can also cause severe, long-term damage to the lungs and lead to respiratory failure (inability to breathe normally) and death. In the pancreas, the thick mucus caused by CF prevents the release of digestive enzymes when you eat. This leads to malnutrition and poor growth. CF can also cause liver disease, reproductive problems, and cystic fibrosis-related diabetes (CFRD). More than 40,000 people in the U.S. live with CF. Doctors diagnose about 1,000 new cases each year. Today, more than half of the CF population is aged 18 or older, and new treatments have expanded the life expectancy by decades.

Source: www.webmd.com ↗
04What Are the Symptoms of Cystic Fibrosis?

The symptoms of cystic fibrosis vary. Some children will have symptoms at birth, while others may not have symptoms for weeks, months, or even years. The severity of symptoms also varies, with some children showing only mild digestive and lung problems and others having severe food-absorption problems and life-threatening breathing complications. The most common symptoms of cystic fibrosis are: Salty-tasting skin , which parents notice when they kiss their child Frequent coughing , wheezing , or bouts of pneumonia or sinusitis Difficulty breathing that keeps getting worse Big appetite but poor weight gain Bulky, smelly, greasy bowel movements Over time, the symptoms of cystic fibrosis can worsen and may include: Chronic productive cough, recurrent lung infections Obstructive lung disease ( emphysema ) Chronic nasal congestion and sinus infections Pancreatitis , a painful inflammation of the pancreas Liver disease Diabetes Gallstones

Source: www.webmd.com ↗
05When to see a doctor

If you or your child has symptoms of cystic fibrosis — or if someone in your family has CF — talk with your healthcare professional about testing for the condition. Make an appointment with a doctor who has skills and experience in treating CF. CF requires regular follow-up with your healthcare professional, at least every three months. Call your healthcare professional if you have new or worsening symptoms, such as more mucus than usual or a change in the mucus color, lack of energy, weight loss, or severe constipation. Get medical care right away if you're coughing up blood, have chest pain or trouble breathing, or have severe stomach pain and bloating. Call 911 or your local emergency number or go to the emergency department at a hospital if: You're having a hard time catching your breath or talking. Your lips or fingernails turn blue or gray. Others notice that you're not mentally alert.

Source: www.mayoclinic.org ↗
Research context

Read sources and limitations before applying a claim.

Research and Statistics: Who Has Cystic Fibrosis?

About 40,000 people are living with cystic fibrosis in the United States, and there are approximately 105,000 people with CF worldwide. (3) More than 75 percent of people with the disease are diagnosed by age 2, and more than half of all people living with cystic fibrosis are 18 or older. CF occurs predominantly in white populations, at a rate of 1 in 2,500 births. Between 2 and 5 percent of white people are carriers of the CFTR gene variant but have no overt clinical signs of disease. The disease is less common among African Americans, occurring at the much lower frequency of approximately 1 out of 17,000 births. (15) CF gene variants are most prevalent in persons of northern and central European ancestries or of Ashkenazi Jewish descent. They are rarely found in Native Americans, Asians, or native Africans. (16) CF is equally common among men and women, but women patients fare significantly worse than male patients with the disease. The median survival age for female CF patients is about three years younger than it is for men, but the reasons for the poorer survival rates among women are not completely understood. (17)

Source: everydayhealth.com ↗
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