A semi-blinded study comparing 2 methods of measuring nasal potential difference: Subcutaneous needle versus dermal abrasion

BackgroundAccording to European and US protocols, two nasal potential difference (NPD) measurement methods are considered acceptable, although they have not been formally compared: subcutaneous agar-filled needle with calomel (Ndl) and dermal abrasion with conducting cream and Ag/AgCl electrodes (Abr). We compared both in CF and healthy volunteers (HV), assessing their discriminative value and subject's preference.MethodsTwelve classic CF and 17 HV underwent both NPD methods, performed by one operator in random order. A written questionnaire, assessing preference, was completed after each test. Tracings were coded, scored in a semi-blinded fashion and categorised as CF/non-CF.Results110 tracings (56 Ndl/54 Abr) were collected: 42/110 scored CF and 68/110 non-CF, showing a good correlation. No significant preference for either method was reported.ConclusionBoth NPD methods are similar in terms of discriminative value and subject's preference, comparing classical CF and HV. For diagnosing CF, the operator's preferred NPD-method may be used.