Sweat test: Also known as the sweat chloride test. A simple test that is used to evaluate a patient who is suspected of having cystic fibrosis (CF). The goal of the test is to stimulate the patient's skin to produce a certain amount of sweat, which may then be absorbed by a special filter paper and analyzed for its chloride content. In a technique called iontophoresis, a small painless electric current is applied to the forearm or back, allowing penetration of a medication that maximizes sweat stimulation. The test result is normal, intermediate, or abnormal.
Patients with CF usually have an abnormally high chloride value in their sweat. Intermediate test results should be repeated. Abnormal tests may be repeated to confirm the diagnosis. Conditions that may produce a false positive test include diseases of adrenal, thyroid, or pituitary glands; some types of glycogen storage diseases, ectodermal dysplasia and atopic eczema. Children with these conditions are generally easily differentiated from patients with CF by their clinical condition. Molecular tests for CF can be done to clarify the situation. See also: Cystic fibrosis.