Advice after your nerve block for surgery
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Your doctor has advised that a sweat test is carried out. This page is intended to give you further information about the test.
What is a sweat test?
A sweat test is a procedure that collects sweat and the laboratory measure the amount of salt in the sweat that is collected.
Why is this being done?
A sweat test is organised when your doctor wishes to rule out Cystic Fibrosis (CF) as a cause of your child's problems. Cystic fibrosis is a chronic disease that mainly affects the lungs and the and the digestive system. Early diagnosis and management of CF can significantly improve outcomes.
Who does the test?
The test will be done by specialist nurses in the Children’s Outpatients’ Department at either Wexham Park Hospital or Frimley Park Hospital.
Does it hurt?
Occasional tingling may be felt in the arm. No needles are involved.
How is the test done?
Special pads soaked in a chemical (pilocarpine) are placed on the lower arm. They are secured and a small electric current is passed through the pad from a battery, to stimulate sweating. Tingling may be felt. The pads are left in place for 5 minutes, then removed. There should be a red mark where the pilocarpine has stimulated the skin – this is usual and will fade within a few hours. The skin is then washed carefully and dried.
A plastic coil is placed on the area and secured. This will stay in place for a period of 20 – 30 minutes, during which time you will need to stay in the outpatients department. The coil system is then removed and sent to the lab for analysis.
What can go wrong?
This is considered a very safe test and is usually well tolerated.
The commonest problem is that an inadequate amount of sweat is collected and the test may need to be repeated at another time. Similarly the test result may not give a diagnosis and the test may need repeating and/or other tests be needed.
A very rare complication (less than 1 in 50'000 test) is some minor burning of the skin when the electric current is applied. If these occur, they usually heal within 1–2 weeks with little or no scarring.
Some children show some sensitivity to the pilocarpine and can have blisters often mistaken for a burn but this resolves in a few hours.
What about the results?
Your doctor will check the result and either inform you personally, or via an outpatient nurse.
Further Questions?
If you have any further questions about the test please don’t hesitate to contact us using the following email: fhft.
Contact us
If you have any queries relating to this information, please contact the Paediatrics service.
About this information
Service:
Paediatrics
Reference:
P/006
Approval date:
18 July 2024
Review date:
1 July 2027
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Important note
This page provides general information only. It is developed by clinical staff and is reviewed regularly every 3 years for accuracy. For personal advice about your health, or if you have any concerns, please speak to your doctor.