Cystic Fibrosis Sweat Test

Cystic fibrosis is detected through an easy procedure called the sweat test.

Sweat test defined

A cystic fibrosis-afflicted person has higher amount of salt (or sodium chloride) in his perspiration than a normal person (up to 5 times more). Salt is a key factor in determining if the person has the disease. The best way to measure salt content is by studying and testing the person’s sweat.

Infancy

The disease can be detected at a young age and the sweat test can be performed on a two-day-old infant. However, there’s likelihood that it may seem inconclusive at this early stage because babies who are less than a month old may not emit the right amount of sweat and may have low chloride levels. Still, it’s better to already know if the baby’s perspiration shows signs of cystic fibrosis at this stage, even though it’s a mere prognosis.

Sweat test procedure

The sweat test usually takes 45 minutes to conduct, and the procedure is simple.

1. The skin is cleansed and afterwards patted till dry. Two small-sized gauze pads are placed at different areas on the skin. One pad contains a medicine known as pilocarpine (to activate salt production). Another pad contains salt water. Electrodes are positioned on top of the two gauzes. The electrodes produce a tiny current, which forces the medicine under the skin to activate perspiration.
2. The gauze pads and those electrodes must stay on the skin for at least five minutes. After they are removed, the skin then gets cleansed and dried again.
3. A dry pad of gauze must be taped on the same area. To prevent evaporation, the pad gets covered with some plastic or wax.
4. The newer pad is left to absord perspiration for around 30 minutes.
5. After the pad is removed, it’s put in a bottle that’s sealed and weighed in a laboratory to measure the amount of chloride in the sweat.

No Major Ill Effects

The test only causes mild discomfort, but no major pain or complications. A tingling sensation may be felt when the electrodes make contact with the skin. To prevent possible electric shock, the gauze pad should be placed on the arm or one’s leg only since these areas are less likely to elicit electrocution.

You may notice a slight reddening of the skin and excessive sweat outbreak where the medicine was placed. In a few instances, the skin may even seem a bit sunburned. This is normal and will subside after several hours.

Results of the sweat test

A patient can pick up the results in one or two days. Results vary depending on the lab, but the general indications are:

• Normal chloride level: below forty (40) millimoles per liter (mmol/L)
• Borderline chloride level: 40–60 mmol/L
• Abnormal chloride level: above 60 mmol/L

Limitations

There may be some reasons as to why results can prove useless:

• Eczema. A mild skin rash may surface in the area where the gauze pads were placed and may progess into eczema, an inflammatory skin condition that may cause severe itching, sweat and infection.
• Dehydration and heavy sweat.
• The opposite may also occur when the patient experiences a significant drop of sweat.
• An acute illness may occur.
• For adolescents, they may experience constant fluctuations in salt due to puberty. This means that results may vary if the adolescent takes the test more than once.
• A drop in aldosterone (a hormone), which is produced by the adrenal glands.
• Intake of steroids may also affect the results. One steroid that can result in faulty findings is fludrocortisone, especially for those who need to take this due to low blood pressure.

The major limitation to the test, however, is that the results don’t indicate what stage the cystic fibrosis is at. The test merely shows if the person is actually carrying the disease. Hopefully, with the wealth of information continuously being gathered, the next steps to detecting the disease through the study of sweat will be discovering the cure.

Disclaimer: This website provides general information about cystic fibrosis and in no means should be taken as a medical or health advice. Please consult your doctor before acting on any of its information.