Sweat Test for Cystic Fibrosis

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.

Why this test is done

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.

How to prepare

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.

Other names for this test

sweat chloride test, cystic fibrosis sweat test, sweat electrolytes