Having a sweat test
This page gives you information about having aa sweat test. It also explains what to expect when your child comes to the hospital for the test.
On this page
Why does this test need to be carried out?
This test is carried out on babies or children for a variety of reasons, such as:
- a history chest infections
- unexplained and unusual loose and pale stools
- problems gaining weight
Your child’s doctor has decided that this test is appropriate because your child’s symptoms indicate that they may have cystic fibrosis. It is important to test children for this condition as soon as possible so that a diagnosis can be made and treatment started.
What is a sweat test?
A sweat test is carried out to collect and measure the amount of salt (sodium chloride) in your child’s sweat. This helps us to assess whether your child might have a condition known as cystic fibrosis, a genetic condition that affects the lungs and the digestive system. The sweat test is used because people with cystic fibrosis have a higher amount of salt in their sweat than normal.
Who will carry out this test?
The test will be carried by a healthcare scientist at Gloucestershire Royal Hospital. You will be able to stay with your child throughout the test.
What happens during the test?
An area of skin on your child’s arm or leg is cleaned with an alcohol wipe and then moistened with ultra-pure water. Special pads, soaked in a chemical called pilocarpine which stimulates sweat production, are then placed on your child’s lower arm or leg. These are secured in place with a bandage and a small painless electric current is passed through the pads from a battery box.
The current is applied for 5 minutes and then the pad is removed and the sweat is sent to the laboratory for analysis. The skin is then washed with ultra-pure water and carefully dried. There will be a red mark where the pilocarpine has stimulated the skin. This is normal and usually fades within 24 hours.
To get an accurate result, enough sweat must be collected, so sometimes the test needs to be repeated on the other arm or leg.
Your child will have to wait with the bandaging in place for 30 minutes while the sweat is collected.
During this waiting time, they can play and eat normally, although salty foods such as crisps should be avoided to reduce any risk of contamination.
Will the test hurt?
No, although some children say that it causes a tingling sensation on the arm or leg where the sweat is collected.
Very rarely (1 in every 50,000 cases) minor skin burns have been reported. When this has happened, the patients showed no sign of pain or discomfort during the test and the skin burns were only discovered when the special pads used were removed from the skin. The burns will heal completely within 1 to 2 weeks with little or no scarring. Please be aware that it is highly unlikely that your child will suffer a burn during the test.
If you have any concerns, you will be able to ask questions to the person performing the test before it begins.
What does the result mean?
If the levels of salts are very low, then cystic fibrosis is extremely unlikely. If the levels are very high, then your child almost certainly does have cystic fibrosis. Your child’s hospital doctor will discuss the implications of this with you. The doctor may also repeat the sweat test to confirm the result and perform some other tests on blood and stool samples. Sometimes, even when enough sweat has been collected, the result can be hard to read and the test may need to be repeated.
How long will it take to get a result?
The result of the test should be available from the laboratory within 2 working days. Your doctor or a nurse specialist will contact you directly as soon as the result is known. It is important to leave a telephone number or some other means of communication with the receptionist.
Further questions
If you have any further questions you should speak to the doctor who referred your child for this test.
How to find the Children’s Outpatient Department
We are based in Gloucestershire Royal Hospital. The sweat test will be carried out in the Children’s Centre. If your child is an inpatient, you need to head for the exit from the wards on the first floor. You will find the Outpatient Department on your left just before the double doors leading out to the stairs and lift.
Alternatively, you can enter the hospital by the dedicated Children’s Department entrance then take the stairs or lift to the first floor. You will find the Outpatient Department on your right just through the double doors.
Contact information
Paediatric Department
Gloucestershire Royal Hospital
Tel: 0300 422 8493
Please leave a message with your child’s full name, date of birth and a contact number.