A small electrode is placed on the skin to stimulate sweat production. The amount of
chloride (a component of salt in the sweat) is then measured. A
chloride concentration greater than 60 mEq/L in sweat on two separate occasions is diagnostic of CF.
- Nasal transepithelial potential difference (NTPD or NPD) testing can be used to assess the function of the cystic fibrosis gene product, a chloride channel called cystic fibrosis transmembrane conductance regulator (CFTR).