Biochemistry
Sweat Tests
Information for patients / parents or guardians
This fact sheet has been produced to provide information for people who have been referred for
a sweat test. In addition, it explains what the results may mean and how you can get the results
of your test.
What is a sweat test?
A sweat test measures the amount of salt (sodium and chloride) that is in the sweat.
Why does this need to be carried out?
The test is carried out on children or adults who are having recurrent chest infections, those that
have frequent and unexplained pale stools or bouts of diarrhoea, and/or those that are having
problems gaining weight or growing properly. Usually the test is performed to exclude the
diagnosis of the disease called cystic fibrosis.
A positive result may mean that you or your child has cystic fibrosis (CF) but a final diagnosis
will take into account other symptoms, clinical findings and test results. People with CF have a
higher amount of salt in their sweat than normal.
A normal result can be helpful in ruling out CF. It is important to diagnose this condition as soon
as possible in order to begin appropriate treatment.
Occasionally patients have had mild symptoms for many years and it is necessary to carry out
sweat tests on older children or adults.
Who does this test?
The test is carried out by a clinical biochemist or biomedical scientist who has been trained in
the procedure.
If you need this information in another format or language 01536 492510
Further information about the Trust is available on the following websites:
KGH - www.kgh.nhs.uk | NHS Choices - www.nhs.uk
Ref: PI.100 July 2014
Review: April 2016
Does the test hurt?
Some people experience a tingling sensation on the arm or leg where the sweat has been
collected. No needles are involved. You will be able to stay with your child throughout the test.
How is the test carried out?
Special pads, about the size of a 50p piece, soaked in a chemical called pilocarpine that
stimulates sweat production are placed on the forearm. These are secured in place and a small
electric current is passed through the pad from a battery box to further stimulate the sweating
process. The pads are left in place for about 5 minutes.
Although the test is not painful, a tingling sensation may occur. However, having to keep still for
5 minutes is difficult for many babies and small children, so it might be useful to bring a favourite
toy or comforter along with you.
The pads are then removed. There will be a red mark where the pilocarpine has stimulated the
skin. This is usual and should fade within a few hours.
The skin is then carefully washed with pure water and dried. A collecting device containing a
plastic coil is placed over the stimulated area and secured.
You will then be asked to wait for about 30 minutes for the sweat produced to be taken up into
the collecting device. During that time you (or your child) are free to read (play) or eat,
(although salty foods such as crisps should be avoided to minimise any risk of contamination).
The collecting device is then removed and the collected sweat is sent to the laboratory for
analysis.
The results
In most cases the results will clearly show either a high (abnormal) or normal salt level in the
sweat. Sometimes the results can be borderline and the test will need to be repeated.
In a few cases the test may need to be repeated for technical reasons such as the inability to
collect enough sweat.
How do I get the results?
If the test has been requested by a doctor at Kettering General Hospital, you can telephone
your consultant’s secretary for the results of the test.
If the test has been requested by your GP, you can phone your GP’s surgery. Alternatively, you
can wait until your next appointment to discuss the results with your doctor.
Results are usually ready 7 days after the test has been performed. The clinical biochemist or
biomedical scientist performing the test will be able to tell you when the results will be ready.
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Further questions
If you have questions about the procedure for a sweat test, please contact the Biochemistry
department on 01536 493385.
If you have further questions regarding the need for a sweat test for yourself or your child,
please speak to the doctor who has referred you for this test as they can give you further
information.
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