Sweat Testing

(Note some patients report feeling mild-to-moderate discomfort in an area about one inch square on the forearm for five minutes during test while others report no discomfort at all during this five minutes period.) The most reliable way to diagnose CF is analysis of the sweat for amount of chloride (salt) it contains. (Note: It is important to have a sweat test using the method approved by the CF foundation for both collection and analysis. “Screening tests” may be unreliable.) The patient’s forearm is thoroughly cleaned and chemical called pilocarpine is placed on the forearm. Two small, battery-powered electrodes are attached. A small current (four mill amperes) from the electrodes forces the pilocarpine into the skin stimulating sweat glands to sweat in that spot on the forearm. Stimulation of the sweat gland takes five minutes. This sweat stimulation feels uncomfortable to some, but many people feel only a tingling sensation. Then a round, plastic disk is taped onto the arm and a piece of gauze is placed under it. The patient wears the gauze patch for 30 minutes to collect the sweat. The gauze is then removed and sent to the lab for analysis of the chloride content. Results of the sweat test are usually available on the date of service. Patients who are sent for a test by a physician outside of ACH must obtain the results from the ordering physician. Patients being seen in an ACH clinic can get results from ACH physician.

A sweat test result higher than 60 mEq/L is considered positive for cystic fibrosis and must be repeated before a diagnosis of CF can be made. Results between 40-60 mEq/L are considered inconclusive and must be repeated as well. Results lower than 40 mEq/L are negative and do not bear repeating.