Sweat chloride test

A simple test used to evaluate a patient who is suspected of having cystic fibrosis (CF). The goal of the 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 chloride content. In a technique called iontophoresis, a minute, painless electric current is applied to the forearm or back, allowing penetration of a medication that maximizes sweat stimulation. Normal sweat chloride values are 10 to 35 milliequivalents per liter; patients with CF usually have a value greater than 60 milliequivalents per liter. Intermediate values (between 35 and 60) may be seen in some CF patients, and in some normal children. In those cases, the sweat test should be repeated in the very near future. In a severely malnourished patient with CF, the sweat chloride may be normal; however, once the malnutrition is corrected, the test will become positive. There are a few rare conditions that produce a false positive test, including diseases of adrenal, thyroid, or pituitary glands; rare lipid storage diseases, and infection of the pancreas. Generally, these children are easily differentiated from patients with CF by their clinical condition, and molecular tests for CF can be done to clarify the situation. Also known as the sweat chloride test. See also cystic fibrosis.