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Nasal potential difference: Best or average result for CFTR function as diagnostic criteria for cystic fibrosis?
Katherine Keenan1, Julie Avolio1, Claudia Rueckes-Nilges2
1Division of Paediatric Gastroenterology, Hepatology and Nutrition, University of Toronto and Physiology and Experimental Medicine, Research Institute, the Hospital for Sick Children, Toronto, Ontario, Canada.
Background:
The current practice of averaging the nasal potential difference (NPD) results of right and left nostril measurements reduce inter-individual variability but may underestimate individual CFTR function.
Methods:
Best NPD response to Cl(-)-free and isoproterenol perfusion (=largest ΔPD(0Cl/Iso)) from the right and left nostril was compared to the average result in 13 cystic fibrosis (CF), 78 query-CF patients and 22 healthy controls from 2 cohorts.
Results:
Despite moderate to good correlation (p<0.001) between right and left measured ΔPD(0Cl/Iso), we observed large differences in some individuals. A comparison of average versus best ΔPD(0Cl/Iso) showed only moderate agreement (Giessen κ=0.538; Toronto κ=0.607). Averaging ΔPD(0Cl/Iso) showed a lower composite chloride response compared to best ΔPD(0Cl/Iso) and altered diagnostic NPD interpretation in 30 of 113 (27%) subjects.
Conclusions:
The current practice of averaging the NPD results of right and left nostril measurements leads to an underestimation of the individual CFTR function and should be reconsidered.
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