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test measures the amount of salt chemicals (sodium and chloride) in sweat. It
is done to help diagnose
cystic fibrosis. Normally, sweat on the skin surface
contains very little sodium and chloride. People with cystic fibrosis have 2 to
5 times the normal amount of sodium and chloride in their sweat.
During the sweat test, medicine that causes a person to sweat is applied
to the skin (usually on the arm or thigh). The sweat is then collected on a
paper or a gauze pad, and the amount of salt chemicals in the paper or gauze is
measured in a lab. Generally, chloride (sweat chloride) is measured. See a
picture of a
A sweat test is done on any person suspected of having
cystic fibrosis. An initial test may be done as early as 48 hours of age. But a
sweat test done during the first month of life may need to be repeated. Younger
babies may not produce enough sweat to give reliable test results. Also,
younger babies may naturally have lower sweat chloride levels than older babies
and children with cystic fibrosis.
The sweat test is done to help diagnose
cystic fibrosis. It also may be used to test people with a
family history of cystic fibrosis and for anyone with
symptoms of cystic fibrosis.
No special preparation is needed before
having this test. Your child may eat, drink, and exercise normally before the
test. If your child takes any medicines, he or she may take them on the usual
You may help with the test and stay with your child
during the test. If you can't stay, you may want to ask a family member or
friend to stay with your child. Bring your child's favorite book or toy to help
pass the time while the test is done. See if your child might be able to watch
a movie during the test.
Talk with your doctor about
any concerns you have regarding the need for the test, its risks, how it will
be done, or what the results will mean. To help you understand the importance
of this test, fill out the
medical test information form(What is a PDF document?). For more information, see the topic Pediatric Preparation for Medical Tests.
The sweat test is usually done on a
baby's right arm or thigh. On an older child or adult, the test is usually done
on the inside of the right forearm. Sweat is usually collected and analyzed from
two different sites.
The sweat test usually takes 45 minutes to 1 hour.
This test does not cause pain. Some
children feel a light tingling or tickling when the electric current is applied
to the skin. If the gauze pads are not properly placed, the electric current
may produce a burning sensation.
There is very little risk of complications from
this test. But the test should always be done on an arm or leg (not the chest)
to prevent the possibility of electric shock.
The electric current
may cause skin redness and excess sweating for a short time after the test is
done. In rare cases, the current may make the skin look slightly
A sweat test measures the amount of salt
chemicals (sodium and chloride) in sweat. Generally, chloride (sweat chloride)
Results are usually available in 1 or 2 days. Normal
results vary from lab to lab.
Less than 40
millimoles per liter (mmol/L)
60 mmol/L or more
Less than 30 mmol/L
Many conditions can change sodium and chloride levels.
Your doctor will discuss any significant abnormal results with you
in relation to your symptoms and past health.
The test results
do not show how severe the cystic fibrosis is. The test only shows if a
person could have the disease.
Reasons your child may not be able to
have the test or why the results may not be helpful include:
CitationsFarrell PM, et al. (2008). Guidelines for diagnosis of cystic fibrosis in newborns through older adults: Cystic Fibrosis Foundation consensus report. Journal of Pediatrics, 153(2): S4–S14.Other Works ConsultedFischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.LeGrys VA, et al. (2007). Diagnostic sweat testing: The Cystic Fibrosis Foundation Guidelines. Journal of Pediatrics, 151(1): 85–89.Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby.
June 15, 2011
John Pope, MD - Pediatrics & Susanna McColley, MD - Pediatric Pulmonology
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