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Chloride Sweat Test



 Submitted by Medical Health Test Team on July 9, 2010
Chloride Sweat Testing

A chloride sweat test is used to diagnose cystic fibrosis (CF). It is also used to confirm CF in patients who have shown indeterminate or positive results with other tests such as nasal (transepithelial) potential difference (NPD) test, immunoreactive trypsinogen test (IRT), a screening sweat test, or the trypsin test. Other tests include the sweat test and is not used to monitor CF as the elevated levels the results show do not have any relation with either the symptoms or the severity of this disease.  The chloride sweat test is generally recommended when a person has symptoms of the disease or has a close relative who has been diagnosed with cystic fibrosis. A baby can also be screened for cystic fibrosis if he/she has tested positive during a new born screening for CF. Patients who have tested negative for CF during a standard CF gene mutation panel but are still thought to have CF, may undergo the test as well.

The sweat test measures the amount of sodium and chloride (sweat chemicals) in sweat. Persons with CF have about 2 – 5 times more than the normal amount of sweat chemicals in their sweat. The chloride sweat test is usually done on the forearm but can be done on the thigh for children or for infants. The first step involves placing two pads on the skin. One is soaked with pilocarpine (a sweat inducing drug) on the skin, the other with salt water. Electrodes are then placed over these pads. After this a small electric current is passed through the electrodes. This helps the drug to stimulate sweat. A small tingling sensation is felt at this time. After about ten minutes, the gauze pads and the electrodes are removed. The skin is cleaned with water and dried. A new dry gauze pad or special tubing is placed on the skin. The pad will either be covered with wax or plastic to prevent evaporation.  After 30 minutes, the pad will be removed and put in a sealed bottle. It will then be checked to see how much sodium chloride the sweat contains. The chloride sweat test usually takes about 45 minutes to an hour.

Results vary from lab to lab. A positive result is when the chloride concentration is greater than 60 milli equivalents per liter. A negative is less than 40. Readings between 40-60 is borderline. This applies to children and adults. For babies, a chloride concentration below 30 is considered normal.

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