What It Is
A chloride sweat test helps diagnose cystic fibrosis (CF), an
inherited disorder that makes kids sick by disrupting the normal
function of epithelial cells, which make up the sweat glands in the
skin and also line passageways inside the lungs, liver, pancreas,
and digestive and reproductive systems. Kids who have CF are more
vulnerable to repeated lung infections.
The sweat test measures the amount of chloride in sweat. Kids
with cystic fibrosis can have two to five times the normal amount
of chloride in their sweat. In a sweat test, the skin is stimulated
to produce enough sweat to be absorbed into a special collector and
then analyzed.
Doctors may test an infant suspected of having cystic fibrosis
as early as 48 hours after birth, though any test conducted during
a baby's first month might need to be repeated because newborns
may not produce enough sweat to ensure reliable results.
Why It's Done
Doctors will order a chloride sweat test for kids with a family
history of cystic fibrosis or symptoms of the disorder. Symptoms
and signs include failure to grow, repeated lung infections, and
digestive problems.
Preparation
No special preparation is necessary for this test. Before having
this test, your child may eat, drink, and exercise as usual, and
continue to take any current medications. A sweat test usually
takes about an hour, so you may want to bring books or toys to help
your child pass the time.
The Procedure
An area of skin on the arm will be washed and dried. Next, two
electrodes are attached with straps (see illustration). One of
these contains a disc with pilocarpine gel, a medication that
stimulates the sweat glands to produce sweat. The medication is
pushed through the skin by an electric current. After this is
completed, the electrodes are removed and the skin is cleansed.
A special sweat collection device (see illustration) is then
attached to the clean skin surface in the area where the sweat
glands were stimulated. It's taped to the skin to keep it from
moving. The sweat that's collected turns blue when it comes
into contact with blue dye within the collector, making it visible
to the technician.
After sufficient sweat accumulates in the tubing inside the
collector, it's removed and placed in the sweat analyzer. The
collector apparatus is removed and the arm is cleaned again. Your
child's skin may remain red and continue sweating for several
hours after the test.
What to Expect
This test shouldn't be painful, though some kids do feel a
slight tingling or tickling sensation when the electrodes apply
current to the skin.
Getting the Results
Results are usually available in 1-2 days.
If your child has a sweat chloride level of more than 60
millimoles per liter, it's considered abnormal and indicates a
high likelihood of cystic fibrosis, though some children with
cystic fibrosis do have borderline or even normal sweat chloride
levels. If results are positive or unclear, a blood test may be
done, especially for babies.
Risks
This test poses very little risk of complications. The
electrical current may cause your child's skin to be red or to
sweat excessively for a short period of time. In rare cases, the
skin may look slightly sunburned.
Helping Your Child
You may choose to stay with your child to help keep him or
her distracted during the test.
If You Have Questions
If you have questions about the chloride sweat test and how
it's conducted, speak with your doctor.
Reviewed by:
Kate M. Cronan, MD
Date reviewed: March 2009
Note: All information is for educational purposes only. For specific medical advice,
diagnoses, and treatment, consult your doctor.
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