What is the sweat chloride test?
The sweat chloride test is a common and simple test used to evaluate a patient who is suspected of having cystic fibrosis (CF), the most common lethal genetic disease affecting Caucasians. Cystic fibrosis is often clinically suspected when there is poor growth during infancy or recurrent serious intestinal or respiratory diseases in a toddler or young child. The genetic defect in cystic fibrosis affects the way chloride moves in and out of cells, and sweat contains chloride in the form of sodium chloride (salt). Measurement of the chloride in sweat has been the standard method for diagnosing cystic fibrosis for over 40 years. Because cystic fibrosis is so common, many states include testing for the cystic fibrosis gene as part of the Newborn Screen; however, sweat testing is still required to confirm the diagnosis.
What is the aim of the sweat chloride test?
The goal of this test is to painlessly stimulate the patient's skin to produce a large enough amount of sweat which may then be absorbed by a special filter paper and analyzed for the content of chloride in the sweat. Patients with cystic fibrosis produce larger quantities of sweat chloride than normal individuals.
How is the sweat chloride test done?
To produce the necessary volume of sweat, a technique called iontophoresis is employed. The technique requires the application of a tiny (painless) electrical current that medically stimulates maximum sweat production.
The patient's forearm is commonly used. However, in small infants, the back may also serve as an appropriate area to perform this procedure.