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Sweat Testing

If a person shows symptoms of CF or if a baby has a positive newborn screen for CF, a doctor may order a sweat test. This simple, painless test is the best way to diagnose CF. It measures the concentration of salt in a person’s sweat. A high salt level indicates CF.

Sweat tests should be done at a Cystic Fibrosis Foundation Accredited Care Center where strict guidelines help ensure accurate results.

Sweat Testing Procedure and Commonly Asked Questions

The sweat test has been the “gold standard” for diagnosing cystic fibrosis (CF) for more than
40 years. When it is performed by trained technicians, and evaluated in an experienced,
reliable laboratory, the sweat test is still the best test to diagnose CF. It is recommended that
the sweat test be performed in a Cystic Fibrosis Foundation-accredited care center where strict
guidelines are followed to ensure the accuracy of the results. The test can be performed on
individuals of any age. However, some infants may not make enough sweat for the laboratory
to analyze. If an infant does not produce enough sweat on the first sweat test, it should be
repeated to collect more.

What happens during a sweat test?

The sweat test determines the amount of chloride in the sweat. There are no needles involved
in the procedure. In the first part of the test, a colorless, odorless chemical, known to cause
sweating, is applied to a small area on an arm or leg. An electrode is then attached to the arm
or leg, which allows the technician to apply a weak electrical current to the area to stimulate
sweating. Individuals may feel a tingling sensation in the area, or a feeling of warmth. This
part of the procedure lasts approximately five minutes. The second part of the test consists of
cleaning the stimulated area and collecting the sweat on a piece of filter paper or gauze or in a
plastic coil. Thirty minutes later, the collected sweat is sent to a hospital laboratory for
analysis. The entire collection procedure takes approximately one hour.

What does the sweat test reveal?

Your physician has asked that this test be performed to rule out the presence of CF, an
inherited disorder of the lungs, intestines and sweat glands. Most children and adults with CF have
an increased amount of chloride (salt) in their sweat. In general, sweat chloride concentrations
less than 40 mmol/L are normal (does not have CF); values between 40 to 60 mmol/L are
borderline, and sweat chloride concentrations greater than 60 mmol/L are consistent with the
diagnosis of CF. For infants under 1 year of age, sweat chloride concentrations less than 30 are considered normal.  For individuals who have CF, the sweat chloride test is most often positive from
birth. Once a test result is positive, it is always positive. Sweat test values for people with CF do not change from
positive to negative or negative to positive, as a person grows older. Sweat test values also do
not vary when individuals have colds or other temporary illnesses.

A negative sweat test does not rule out the possibility of Cystic Fibrosis. There are some mutations that may result in a normal sweat value but the person still has clinical signs and symptoms of Cystic Fibrosis.

Is there any preparation for the sweat test?

There are no restrictions on activity or diet or special preparations before the test. However,
one should not apply creams or lotions to the skin 24 hours before the test. All regular
medications may be continued and will have no effect on the test results.

Generally, we recommend you bring extra clothing and blankets to warm your child so he/she will sweat more easily.


When are sweat test results made available?

Sweat test results are usually available in our physician's office the same day as the test was performed and can be provided to your physician on the next working day after the test is performed. In a small number of cases, the quantity of sweat obtained is not sufficient to give an accurate result, and the test may need to be repeated.

Can the test results be inconclusive?

Yes. In a small number of cases, the test results fall into "negative" or “borderline” range between not
having CF and indicative of CF. In these situations, repeat sweat tests, as well as other
diagnostic procedures, may need to be carried out. These will only be done after consultation
with a physician.

 

For more information about the CF Foundation and the programs and services available to people with the disease,
or to learn how you can volunteer and help make a difference, please visit www.cff.org or call (800) FIGHT CF.