How It Feels
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.
Sweat chloride in people age 6 months and older
Less than 40
millimoles per liter (mmol/L)
60 mmol/L or more
Sweat chloride in babies younger than 6 months
Less than 30 mmol/L
60 mmol/L or more
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.
Abnormal (high) values
- Usually mean a person has cystic fibrosis.
Some people with cystic fibrosis have borderline or even normal sweat chloride
- May be caused by other conditions. But the sweat test is
not used to diagnose these conditions, which include:
What Affects the Test
Reasons your child may not be able to
have the test or why the results may not be helpful include:
- A baby's age. Babies younger than 4 weeks may
not produce enough sweat to give reliable test results and may have lower sweat
chloride levels than older babies and children. A minimum amount of sweat is
needed for accurate test results regardless of the child's age.
skin rash or sore on the area of the skin where the gauze pads are
- Acute or severe illness.
Dehydration or heavy sweating.
- Normal fluctuations in sodium and chloride during
- A decrease in the hormone aldosterone.
medicines, such as fludrocortisone.
What To Think About
- Usually, two sweat tests are done to confirm a
- A sweat test can't identify
carriers of the cystic fibrosis gene. If your child is
diagnosed with cystic fibrosis, you may wish to talk with your doctor about
genetic counseling. For more information, see the
Cystic Fibrosis Carrier Screening.
generally have higher salt concentrations in their sweat than children. Also,
sweat test results in adults can vary widely. This is especially true in women,
because the amount of salt in their sweat can vary with the phase of their
menstrual cycle. Enough sweat must be collected to get
accurate test results.
- If results of a sweat test are positive or
unclear (especially in babies), a blood test may be done to detect changes in
the genetic material (DNA) that causes cystic fibrosis. Blood
test results are usually ready in 10 to 21 days. For more information, see the
- Sweat tests should be done
at labs that are certified by the Cystic Fibrosis Foundation (www.cff.org). These labs
perform a large number of sweat tests and are skilled at sweat test techniques