What Is a Sweat Electrolyte
A sweat electrolyte test detects the
amount of sodium and chloride in your sweat. It’s also called an iontophoretic
sweat test or chloride sweat test. It’s used primarily for people who have
symptoms of cystic fibrosis (CF).
The body’s natural chemistry requires
the right balance of sodium and chloride. These chemicals help regulate fluid
in the tissues. People with cystic fibrosis have a mutation on chromosome 7
that affects a protein called the “cystic fibrosis transmembrane conductance
regulator (CFTR).” This protein regulates the movement of chloride and sodium
through the body.
When the CFTR protein
doesn’t work properly or doesn't exist, chloride isn’t able to move through the
body the right way. This causes an abnormal amount of fluid in the lungs, small
intestines, pancreatic ducts, bile ducts, and skin. People with CF have large
amounts of chloride and sodium in their sweat. They can have two to five times
more than other people.
Why the Sweat Electrolyte
Test Is Used
Your doctor may order this test if you
have symptoms of CF. These symptoms include:
- chronic cough
- infertility in
some adult males
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.
Preparing for a Sweat
You don’t need to do much to prepare
for this test. Avoid applying any creams or lotions to the skin 24 hours before
If you have a small child, it’s a good
idea to bring along some activities or toys to keep them occupied during the
Sweat Electrolyte Test
During the sweat electrolyte test, the
clinician will place two electrodes on your upper arm. In infants, the
electrodes are normally placed on the thigh. Each electrode is covered with a
piece of gauze that’s been soaked in a drug called pilocarpine, which
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
keep it sealed and keep the sweat from evaporating. After an hour, the
clinician will remove the 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.
Are There Any Risks
Associated with a Sweat Electrolyte Test?
There are no risks associated with
this test. The electrolyte sweat test is not painful. 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.
Sweat Electrolyte Test
It may take one or two days to get
test results from the electrolyte 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 may need to
The sweat electrolyte test is very
reliable and accurate. It's the gold standard in diagnosing cystic fibrosis.
Since cystic fibrosis can lead to other complications, it’s very important to
detect it early.