Sweat Test Patient Information

WHAT IS A SWEAT TEST?

A sweat test measure the amount of salt (made of sodium chloride) that is in sweat produced during the testing. A special chemical which is known to cause sweating is put on the skin. The amount of salt in the sweat is then analyzed at the point-of-care. This can help to diagnose cystic fibrosis.

WHAT IS A SWEAT TEST USED FOR?

This test is most commonly done to check whether a person has cystic fibrosis. The test may be carried out on patients who are having symptoms which might suggest they have cystic fibrosis such as:

• Diagnosis of bronchiectasis under the age of 40 years
• Unexplained malabsorption and/or malnutrition
• Recurrent chest infections along with family history of cystic fibrosis

Rarely, a sweat test may be carried out for other reasons.

HOW DOES SWEAT TEST WORK?

Cystic fibrosis is a genetic disorder. This means that you are born with it and it is passed on through families through special code inside cells called genes. If you have cystic fibrosis, a particular pair of genes (on chromosome 7) does not work properly. This pair of genes helps to control the way the cells handle salt (sodium and chloride ions). There are many different abnormalities (mutations) of the cystic fibrosis gene. They all stop the cell from dealing with sodium and chloride properly.

When people who have this faulty gene sweat, the pores of the skin can’t soak up the right amount of sodium and chloride. This means that there is more sodium and chloride left on the skin than with a person who doesn’t have this condition. The sweat tests looks for excessive amounts of sodium chloride left on the skin following sweating.

In sweat test, a chemical pilocarpine is placed on the skin. This causes the skin to sweat. An electrode is placed on the skin at two points. A very small electric current is passed between the electrodes.This helps to draw the pilocarpine into the skin and produce sweating. After a while, the area of skin is cleaned and a plastic coil is placed on the skin. After 30 minutes, the plastic coil is removed, tested immediately by the nurse and inform the doctor.

WHAT HAPPENS DURING SWEAT TEST?

The pilocarpine discs are secured in place on your arm. A small electrical current is passed through the pad from a battery box to stimulate the sweating process further. Some people experience a tingling sensation at this point of the test but it should not be painful. No needles are involved. The pads are left in place for about five minutes and then removed. There will usually be a red mark where the pilocarpine has stimulated the skin. This normal and should fade within a few hours. The skin is then carefully washed with pure water and dried. A plastic coil is placed over the stimulated are and secured.

You will then be asked to wait for about 30 minutes for the sweat to be absorbed into the coil device. During that time, you are free to read, eat etc. Salty foods such as crisps should be avoided to minimize any risk of contamination. The plastic coil is then removed and processed immediately by the nurse. You will need to wait until testing is complete. This is to ensure a valid result is obtained and unnecessary repeat visits are required.

WHAT WILL THE RESULTS SHOW?

In most cases, the results will clearly show either 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 not enough sweat is collected. Some doctors like to confirm an abnormal sweat test with a second sweat test.

WHAT SHOULD I DO TO PREAPRE FOR A SWEAT TEST?

Do not use any creams or lotions on the skin for a day before the test.

ARE THERE ANY SIDE EFFECTS OR COMPLICATIONS FROM A SWEAT TEST??

The test is not harmful. Some people feel a small tingling sensation. There may be a small red area where the test has been carried out. This settles very quickly.

CONTACT INFORMATION

Dr. Irfan Shafiq, Pulmonary Clinic, Cleveland Clinic Abu Dhabi