Sweat test
Information for parents from the Pathology Department
What is a sweat test?
A sweat test measures the amount of salt present in a person’s sweat. A small amount of sweat is collected from the lower arm. It may be necessary to use the upper leg in very small babies.
The test is usually done on children who have had frequent chest infections or unexplained bouts of diarrhoea, or children who are not gaining weight or growing normally. It may also be done on babies to follow-up one of the newborn blood spot tests.
Your doctor will consider the possible causes for these symptoms and may arrange a sweat test to confirm that a condition called cystic fibrosis is not the cause.
Where do I go?
A date and time will be arranged by the ward staff for you to come to Kent and Canterbury Hospital. On the day of the test, please come to the reception desk at the Children’s Assessment Centre.
Directions and maps are available on the Trust website.
Is there anything I need to bring to the hospital?
Clothing: please bring a long-sleeved top that is easy to get on and off.
Toys: a favourite toy or game, story book, or tablet may help your child to sit quietly for the first part of the test and distract from the tingling feeling.
Babies may be breast or bottle fed during the test.
How long will we be in hospital?
The test should only take about one hour, after which you can go home.
What will happen during the test?
The sweat sample will be collected by specially trained nurses. It is collected using a special sweat stimulation procedure.
Two pilocarpine gel discs (used to induce sweating) are placed on a clean area of skin on your child’s arm or leg. In order to get the pilocarpine into the skin, the area is stimulated using a small electrical current from a torch battery. Your child should sit quietly. This takes about five minutes.
The area is then cleaned and a small plastic device that looks like a wristwatch is strapped over the area, where one of the gel discs was in contact with your child’s skin.
This is left in place for about 30 minutes to collect your child’s sweat. You should encourage your child to be active to help sweating. Long sleeves help to hide the ‘wristwatch’ device.
The ‘wristwatch’ device containing the sweat is sent to the laboratory to measure the amount of salt in it.
Some children do not sweat readily, particularly those with eczema, and it may be necessary to repeat the test on another limb (arm or leg) or maybe even to come back for a further appointment.
Will it hurt?
The procedure may produce a slight tingling or warm sensation but is not painful. The area of skin which was stimulated may stay red for a few hours, but this is normal and nothing to worry about.
In rare cases (about one in 50,000) there is a risk of a minor burn (Wescor Inc. 1999).
How will I find out the results?
The results of the test will be sent back to the doctor who requested the test. Your doctor will let you know the results when they are available. Laboratory staff are not allowed to give out results on the telephone.
Where can I get more information?
If you have any further questions about why this test is being done, please speak to the doctor or consultant who requested the test.
If you have practical questions about your appointment, please phone the Children’s Assessment Centre, Kent and Canterbury Hospital, Canterbury on 01227 864052.