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Reproducibility of Nasal Potential Difference Measurements in Cystic Fibrosis^*

^* From the Cystic Fibrosis Center (Ms. Yaakov, Dr. Kerem, Ms. Bdolah-Abram, and Dr. Wilschanski), Hadassah University Hospital, Jerusalem, Israel; Cystic Fibrosis Center (Dr. Yahav), Sheba Medical Center, Tel Hashomer, Israel; Cystic Fibrosis Center (Dr. Rivlin), Carmel Medical Center, Haifa, Israel; Graub Cystic Fibrosis Center (Dr. Blau), Schneider Children’s Hospital, Petach Tiqva, Israel; Cystic Fibrosis Center (Dr. Bentur), Rambam Medical Center, Haifa, Israel; Cystic Fibrosis Center (Dr. Aviram), Soroka Medical Center, Beer Sheva, Israel; and Cystic Fibrosis Center (Dr. Picard), Shaare Zedek Medical Center, Jerusalem, Israel.

Correspondence to: Michael Wilschanski, MBBS, Director Pediatric Gastroenterology Unit and Electrophysiology Laboratory, Hadassah University Hospital, Mount Scopus, Jerusalem, Israel 91240; e-mail: michaelwil{at}hadassah.org.il

Abstract

Background: Nasal potential difference (NPD) measurement has been advocated as a diagnostic tool for cystic fibrosis (CF) patients and as a method for assessing the response to new therapies. The purpose of this study was to examine the reproducibility of NPD measurements performed in a single center.

Methods: A total of 68 CF patients with a mean (± SD) age of 16 ± 8 years (age range, 6 to 52 years) underwent NPD measurements on at least two occasions.

Results: A total of 25 patients with classic CF (mean age, 21 ± 8 years) and 43 patients with nonclassic CF (mean age, 14 ± 8 years) underwent sweat tests and NPD measurements. The mean sweat chloride values were 102 ± 18 and 54 ± 14 mEq/L, respectively, for classic CF and nonclassic CF groups. All patients underwent repeat NPD measurements. The basal NPD and the response to amiloride (Amil) and response to Cl^– free and isoproterenol (Cl^– free + iso) were very similar in both measurements. In the classic CF group, the basal potential difference values were –40 ± 12 vs –39 ± 11 mV (p = 0.57), respectively, for the first and second measurements; 27 ± 9 vs 26 ± 10 mV (p = 0.55), respectively, for Amil; and 2.1 ± 3.8 vs 0.4 ± 2.9 mV (p = 0.07), respectively, for Cl^– free + iso. In the nonclassic CF group, the values were –32 ± 13 vs –28 ± 10 mV (p = 0.008), respectively; 19 ± 10 vs 17 ± 8 mV (p = 0.388), respectively; and –3.2 ± 4.6 vs –3.3 ± 4.4 mV (p = 0.876), respectively.

Conclusion: When performed in a single center, NPD is a reproducible test for CF patients and thus may be a useful outcome measurement for assessment of the efficacy of new treatments.

Key Words: cystic fibrosis • nasal potential difference • nonclassic cystic fibrosis