Sweat Test

What is a sweat test?

A sweat test determines the chloride levels in sweat, which is a component of salt found in sweat. This test is instrumental in diagnosing cystic fibrosis (CF) as individuals with CF tend to have elevated chloride levels in their sweat.

CF is a hereditary condition that can impact individuals of all age groups. The presence of CF requires inheriting a modified CFTR gene from both parents. Variations or mutations in genes can also be referred to as changes. If only one altered gene is inherited, the individual becomes a carrier without developing the disease. However, carriers can pass on the changed gene to their children, potentially resulting in CF if both parents are carriers.

The disease primarily affects organs responsible for producing mucus and sweat. Typically, mucus acts as a lubricant and shields the linings of airways, digestive tract, and other bodily organs and tissues. In CF, mucus becomes thick and sticky, leading to accumulations in organs and subsequent damage.

CF predominantly impacts the lungs, causing difficulty in breathing, recurrent lung infections, and lung damage due to thick mucus buildup. Malnutrition is another common concern in CF, as the disease may hinder the body's ability to absorb nutrients effectively from food.

Alternative names for the sweat test include sweat chloride test, cystic fibrosis sweat test, and sweat electrolytes test.

What is it used for?

A sweat test is used to diagnose cystic fibrosis.

Why do I need a sweat test?

A sweat test is an essential diagnostic tool for cystic fibrosis (CF) in individuals of all ages:

Newborns in the United States undergo newborn screening for various conditions, including CF. If a screening test indicates potential CF in a baby, a sweat test is required to confirm the diagnosis. Ideally, the test should be conducted between 10 days and 4 weeks of age. Early initiation of treatment can significantly delay or prevent CF-related health complications.

Children and adults may undergo a cystic fibrosis sweat test if they exhibit CF symptoms or have a family history of CF. While most individuals with CF experience symptoms, some may not. In milder cases, symptoms may not manifest until adulthood. CF symptoms vary depending on the affected organs and may include:

• Wheezing or coughing with mucus or blood production.
• Clubbing of fingers and toes, characterized by wide and rounded nails, indicating low blood oxygen levels due to lung impairment.
• Fever, often accompanied by night sweats.
• Digestive issues like severe abdominal pain, chronic diarrhea, or constipation.
• Underweight or failure to thrive.
• Muscle and joint pain.
• Delayed growth or puberty.
• Salty skin and sweat.
• Sinus infections.

Prompt testing is crucial if CF is suspected. Although there is no cure for CF, early diagnosis and treatment can significantly improve quality of life and longevity for individuals with CF or those at risk.

What happens during a sweat test?

To conduct a sweat test, a healthcare provider will follow these steps, which typically take about an hour:

• Application of an odorless chemical (pilocarpine) on a small area of the forearm or leg to induce sweating. An electrode is then taped over this area.
• A mild electrical current passes through the electrode to facilitate the penetration of the chemical into the skin. This might cause a slight tingling or warmth sensation.
• After approximately 5 minutes, the electrode is removed, and sweat is collected either by taping a piece of filter paper or gauze onto the area or using a small plastic coil.
• Sweat collection continues for 30 minutes.
• The collected sweat sample is sent to a laboratory for analysis.
• In some cases, especially with babies, there may not be enough sweat for a conclusive test on the first attempt. If this occurs, the test is typically repeated on another day.

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

No specific preparations are required for a sweat test, but it's important to refrain from applying creams or lotions to the skin for at least 24 hours before the test.

Are there any risks to the test?

A sweat test carries no known risks. You may feel a tingling or tickling sensation from the electric current of the electrode, but it is not painful.

What do the results mean?

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

• A chloride level of 60 or higher indicates a high likelihood of cystic fibrosis (CF). To confirm the diagnosis, your healthcare provider may recommend repeating the test or conducting a CF genetic test.
• A chloride level of 30 to 59 requires further testing as the result is inconclusive, and CF is a possibility. Your provider may order another sweat test or different testing methods, such as genetic testing.
• A chloride level below 29 is considered normal, indicating a low likelihood of CF. However, a normal result doesn't completely rule out CF, as some individuals with CF can have normal sweat test results. If you or your child show symptoms of CF or had an abnormal newborn screening for CF, additional testing may be necessary.