Sweat test for cystic fibrosis

Introduction

A sweat test is used to diagnose a genetic condition called cystic fibrosis. Cystic fibrosis causes thick, sticky mucus in the body that affects the lungs and the digestive system.

While there is currently no cure for cystic fibrosis, diagnosing the condition early can help children access treatment to improve their quality of life.

A sweat test can be done to measure the amount of salt in a child’s sweat.

Children with cystic fibrosis will usually have a higher amount of salt in their sweat than other children. 

The sweat test is done in the outpatient department at the hospital.

No special preparation is needed before the test. Children can eat, drink, and take any medications they would normally have.  

The sweat test is simple. It involves taking a small sample of your child's sweat from their arm or leg.

The test will usually take around an hour to complete but may be longer if another sample needs to be taken.

Generally, the steps of the sweat test are:

1. your child sits in the testing room that may be warmed up
2. a small area on their arm or leg is cleaned with alcohol wipes and then again with distilled water
3. two small electrodes containing a special gel are put on the clean skin
4. a gentle electrical current is run through the electrodes for around five minutes 
5. the gentle electrical current helps the gel get through the skin and into the sweat glands, causing a slight tingling feeling
6. the electrodes are taken off the skin
7. a sweat-collecting disc is placed over the area and held in place with a bandage
8. your child will sit while the sweat is collected over 20-30 minutes.

Some children may find the skin tested is pink or red for a few hours afterwards. 

Babies under six weeks old can have sensitive skin and some inflammation after the test. This is rare in older children.

Very rarely, small surface burns have happened when the skin is heated under the electrodes. Speak to your child’s doctor if you have concerns about the test.

After enough sweat is collected, it is sent to the lab and tested. 

Your child will be able to go home after the test is finished.

The doctor will usually be able to give the test results on the same day it was done. 

In most cases, a high salt content of more than 60 millimoles per litre can confirm cystic fibrosis.

Your child’s doctor will discuss the results with you and answer any questions you have about the condition and treatments.