Sweat Test

Overview

The “sweat test” is the procedure used for diagnosing cystic fibrosis (CF). The test can be performed on individuals of all ages. However, sometimes infants do not make enough sweat for the laboratory to analyze. If this is the case, the test would have to be repeated. This test is best performed at an accredited CF center.

What happens during a sweat test?

This test measures the amount of salt (sodium and chloride) in the sweat to determine whether a child has CF. Normally, sweat has very little sodium and chloride in it. In cystic fibrosis there is 2-5 times the normal amount of these chemicals in the sweat. The test is done in two steps. In the first step, a colorless, odorless chemical (known to cause sweating) is applied to two small areas on the arm or leg. An electrode is then attached to the one of the areas. This electrode allows the technician to apply a weak electrical current to the area which causes sweating. There may be a tingling or warm feeling in this area. The electrode stays in place for about 5 minutes and will be repeated for the second area being tested. The second part of the sweat test involves cleaning the areas and collecting sweat on a piece of gauze or into a plastic coil. After thirty minutes, the collected sweat is sent to the laboratory for analysis. This entire process takes about one hour. It involves no needles.

What does the sweat test show us?

This test is done to diagnose cystic fibrosis (CF), an inherited disorder that affects the lungs, intestines, and sweat glands. For children over 6 months of age, a sweat chloride concentration less than 40mmol/L is normal, 40-60mmol/L is borderline, and 60mmol/L and above is positive for CF. Individuals with CF will have a positive (greater than 60mmol/L) sweat concentration from birth.  Infants may be considered to have a positive sweat test at lower values than older children.

Preparation

There are no diet or activity restrictions prior to the test. No lotions or creams should be applied to the skin 24 hours before the test. All regular medications both prescribed and over the counter may be continued and will have no effect on the test.

Results

The sweat test must be completed before 11:30 am and the results of the sweat test will be available to the doctor by 4:00pm the afternoon of the day you complete the test. In some cases, the quantity of sweat obtained is not enough to give an accurate result. In this case the test may need to be repeated. If the test falls into the “borderline” category (40-60mmol/L), repeat sweat tests or other diagnostic tests may be needed. Please call (352) 273-8381 for results.

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