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Sweat test in cystic fibrosis

Cystic fibrosis is a genetic disease that affects the whole body, leading to disability and causing lethal consequences. The disease, also known as simply CF or mucoviscoidosis, is caused by mutation of gene controlling sweating, mucus and digestive enzymes. The disease is autosomal recessive condition, which means that it is only expressed if we received two copies of the mutated gene from our parents. If one gene is normal, the patients won’t get cystic fibrosis.

CF Symptoms and Therapy

First symptoms or CF are breathing problems, but the patients often experience growth difficulties, sinus infections and diarrhea. Infertility might also be caused by this disease. CF affects the exocrine glands, especially sweat glands and they don’t absorb the chloride as they should be. As the result, people suffering from CF have extremely high concentration of chloride in the sweat.

Cystic fibrosis is a disease common among Caucasian population, and there is about 30.000 Americans suffering from this serious disease.

There is no cure for CF. Patients are treated for their airway infections, gastrointestinal and reproductive problems, along the psychological support. Transplantation and gene therapy are also possible treatment options for cystic fibrosis patients.

Diagnostic Test for CF

CF can be diagnosed before and after the birth. Unborn children’s diagnosis is established through the genetic testing, while cystic fibrosis in babies, children and adults is diagnosed after a sweat test. Sweat test goal is to measure the level of chloride in sweat. These days, sweat test has become test for newborn children, done just several days after the birth.

During the procedure, two gauze pads are placed on the forearm, one soaked with salt water and the other with pilocarpine. The pads are connected with electrodes, and through them, the doctor will pass some mild electric current for 10 minutes, in order to increase the absorption of pilocarpine and induce sweating. After that, the pads and electrodes are removed, and some filter paper is placed on those exact spots. The filter paper is firstly weighted and covered with some paraffin and left to collect the sweat for 30 to 40 minutes. After that time, doctors will weigh the paper again and calculate the amount of the sweat and then run some tests to determine the level of chloride and sodium in the sweat.

The test is considered to be 98% accurate and it doesn’t cause any discomfort or pain. Only potential unpleasant effect might be transient redness of the skin or increased sweating for some time after the testing.

Test Results

Results which measured more than 60mEq/l (milli equivalents per liter) of chlorides in the sweat are indicating cystic fibrosis. Borderline results are between 40 and 60mEq/l and less than 40mEq/l (or 30 in babies) are considered to be normal results.

Borderline patients are usually tested one more time and there are some molecular tests, designed to confirm CF diagnosis.

Several conditions might interfere with the sweat test results. This include: pancreas infection and thyroid and pituitary gland problems. These conditions can be easily diagnosed and they are rarely (or never) confused with cystic fibrosis.

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