What is the role of nasal potential difference testing in the workup of cystic fibrosis (CF)?

Updated: Oct 30, 2018
  • Author: Girish D Sharma, MD, FCCP, FAAP; Chief Editor: Kenan Haver, MD  more...
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Answer

Potential difference (PD) in voltage measured from nasal mucosa and the reading obtained by a reference electrode inserted into the forearm correlates with the movement of sodium across cell membranes, which is a physiologic function rendered abnormal by a CFTR mutation. The nasal PD (NPD) is a sensitive test of electrolyte transport that can be used to support or refute a diagnosis of CF.

A normal mean value standard error (SE) is 0.9-24.7 mV; an abnormal value is 1.8-53 mV. When measurements are repeated after mucosal perfusion with amiloride to block an epithelial sodium channel, the drop in PD is greater in patients with cystic fibrosis (73%) than in control subjects (53%). Subsequent perfusion with chloride-free solution and isoproterenol produces a sharp increase in the PD in normal subjects but has little effect when CFTR function is abnormal.

As a result of the lack of commercially available equipment and the practical difficulties with NPD measurement, this test is performed in only a few research centers to diagnose CF in patients in whom making a diagnosis is difficult or a sweat test is not technically possible because of skin problems.


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