The nasal potential difference test (nasal PD test) measures how well salts (sodium and chloride) flow across the mucous membranes in the nose. This type of test can be helpful when the results of a sweat test or a genetic test are not clear.

In this test, electrodes are placed inside the nose and liquids are run through the nose. There is also a needle placed in the forearm that connects to a machine. Because this test can be uncomfortable, your child may need medications to help him or her relax before having the test.

Currently, this test is not used very often because it can be difficult to do and because it is not available in many places.