The sweat electrodes test is a test that detects the amount of sodium and chloride in a person’s sweat. This test, which is also called the “iontophoretic sweat test,” is used primarily for patients that have symptoms of cystic fibrosis (CF).
Your care provider may order this test if you have symptoms of CF, which include frequent respiratory infections and chronic cough, continual diarrhea, malnutrition, and in some adult males, infertility.
This test is usually performed on children with suspected symptoms of CF. Because this condition is hereditary, a child with a close relative with CF may also be tested.
The body’s natural chemistry requires the right balance of sodium and chloride. These chemicals help regulate fluid in the tissues. Individuals with cystic fibrosis have a mutation on chromosome 7 that affects a protein called the “cystic fibrosis transmembrane conductance regulator (CFTR),” which regulates the movement of chloride and sodium through the body.
When the CFTR protein doesn’t work right or is absent, chloride isn’t able to move through the body properly. This causes an abnormal amount of fluid in the lungs, small intestines, pancreatic ducts, bile ducts, and skin. Consequently, individuals with cystic fibrosis have large amounts of chloride and sodium in their sweat—often two to five times more than other individuals.
There is no preparation needed for the test. Avoid applying any creams or lotions to the skin 24 hours before the test.
If you have a small child, it’s a good idea to bring along some activities or toys to keep them occupied during the test.
During the sweat electrodes test, the clinician will place two electrodes on the upper arm in children or adults. In infants, the electrodes are normally placed on the thigh. Each electrode is covered with a piece of gauze that has been soaked in a drug called pilocarpine, which stimulates sweating.
Once the electrodes are attached, a small electrical current will flow to the site for five to 12 minutes. The clinician will then remove the electrodes, wash the arm or leg with distilled water, and place a paper disk over the test site.
Next, the disk is covered with wax to seal the site and keep the sweat from evaporating. After an hour, the clinician will remove disk with the sweat and send it to a lab for analysis of the amount of sodium and chloride.
Overall, the electrode sweat should take 90 minutes.
In addition to the sweat electrode test, your provider may request a sweat chloride test, also called a “chloride screening test.” This test can detect sweat chloride levels in a person’s body by using a chemical called silver nitrate.
In this test, the clinician will press a piece of paper with silver nitrate against your hand for several seconds. If you have excess amounts of chloride, it will cause the paper to turn a white-silver color, leaving a clear handprint. This screen is done to determine if there is a need for the sweat electrode test, which will help confirm whether or not cystic fibrosis is present.
The sweat chloride screen takes only a few minutes.
There are no risks associated with this test. Neither the electrode sweat test nor the chloride sweat test are painful. However, you may feel a slight tingle as the electrodes pass a small current through the site where they are attached. The area may still sweat after the test is finished, and the testing area may be red for a brief period.
It may take one or to days to obtain test results from the electrode sweat test.
For infants 6 months and under, a chloride level of 29 mmol/L or less indicates CF is unlikely. A chloride level above 60 mmol/L means it is likely that the child has CF. If the chloride level is between 20 and 59 mmol/L, it means that CF is possible and the test could need to be repeated.
Children and Adults
For children and adults, a chloride level of 39 mmol/L or less indicates CF is unlikely. A chloride level above 60 mmol/L means it is likely that the child has CF. If the chloride level is between 40 and 59 mmol/L, it means that CF is possible and the test could need to be repeated.
The sweat electrodes test is very reliable and accurate, and is the gold standard in diagnosing cystic fibrosis. Because cystic fibrosis can lead to other complications, early detection and treatment is very important.