Reasons, Methods and Results For Cystic Fibrosis Sweat Test

Submitted on March 27, 2012

What is Cystic Fibrosis?

Cystic fibrosis is a genetic disorder, usually considered an inherited disease of the secretory gland, also known as the glands that make mucus and sweat. Cystic fibrosis (CF) disease is medically also referred to as mucovoidosis or mucoviscidosis. Typical symptoms of CF disease include tangibly salty sweat, poor or lack of growth, and weight gain despite a healthy appetite, frequent respiratory and chronic cough infections. Among men, this disease can also cause infertility. Being a genetic disorder, the symptoms for this disease usually show up in early childhood.

Since this disease affects the sweat glands, a sweat test for cystic fibrosis is considered to be among the more reliable tests to aid diagnosis of this disease. There are of course newer and modern methods like genetic testing available, but the sweat test is still by and large the preferred choice.

Reasons To Conduct a Cystic Fibrosis Sweat Test

A doctor orders a CF sweat test in two scenarios; one being, when a newborn baby shows a positive result for CF or two; a person shows symptoms of cystic fibrosis.

The CF sweat test is usually administered only in the arms or thighs of the patient. During this test the area to be tested is washed and dried and then dabbed with sweat inducing medicine. Then two pads (also dubbed electrodes) are placed on the patches of skin through which electric current is passed to ensure the sweat medicine is absorbed into the skin.

Method Used

After about ten minutes or so the electrodes are removed, the area is once again washed and dried, and another piece of gauze pad or any other sweat absorbing material is taped to the patches of the skin. This pad remains on the skin for about half an hour to ensure that enough sweat is collected for diagnosis.

This sweat pad or gauze pad is then sent to the lab to measure the level of chloride and sodium in the sweat. A person with CF disease is known to have nearly two to five times more chloride in their sweat than a non-CF person.

Do note, when the electric current passes through the skin, the patient does feel a tingling or ticklish sensation. However, if the patient feels a burning sensation, it means that the electrodes haven't been appropriately placed on the skin.

Once the CF sweat test is concluded, it is normal for the tested patches of skin to have a red look for a few hours. Also, the area will continue to sweat profusely for a few more hours. At times, the tested skin looks sunburnt for a day or two. But apart from this, the patient should not feel any pain or soreness from the test.

Test Results

While the sweat test has an accuracy rate of 98 percent it is quite likely that sometimes the results may be inconclusive. One reason for this being not enough sweat collected for the test; the other reason could be that the individual may have edema, also known as fluid retention in the body, which dilutes the sweat. Results can also be inconclusive when testing a newborn that's less than a week old.

There are exceptions to every rule and the same holds true for a CF sweat test but by and large if you suspect CF, this test is a pretty reliable, convenient and cost-effective diagnostic tool.