A modified technique for measurement of nasal transepithelial potential difference in infants.

OBJECTIVE: To establish a method for measuring nasal transepithelial potential difference (PD) in infants. STUDY DESIGN: A modified infant method (smaller catheter size, reduced flow rates, and shorter protocol time) was compared with an established adult nasal PD method in 10 adult volunteers (4 with cystic fibrosis [CF]). Nasal PD was measured in 13 infants with a possible diagnosis of CF. RESULTS: Recordings were similar for the established and the modified methods in adult volunteers. An amiloride concentration of 10(-4) mol/L was necessary for full inhibition of amiloride-sensitive sodium ion (Na(+)) transport. Of the 13 infants, 2 had PD values suggestive of CF (mean baseline PD, -50.1 mV and -31.4 mV; maximum baseline PD, -61 mV and -49 mV; change in PD after perfusion with zero chloride solution with isoprenaline and amiloride [DeltazeroCl(-)/Iso], -1 mV and +3.5 mV), and 11 had normal values (mean +/- SEM baseline PD, -13.2 +/- 1.0 mV; maximum baseline PD, -21.4 +/- 2.0; DeltazeroCl(-)/Iso, -15.3 +/- 1.9 mV). These results correlated with subsequent sweat test data, mutation analysis, and clinical outcome. CONCLUSION: Nasal PD measured with this modified method is comparable to that measured with an established adult method. The measurements were well tolerated in 13 infants and discriminated bioelectric profiles characteristic of normal and CF respiratory epithelium. This study supports the use of this modified nasal PD technique as a diagnostic test for CF in newborn infants.

Sweat testing for the diagnosis of cystic fibrosis: practical considerations.

Most pediatricians eventually encounter a patient with a clinical presentation that warrants the consideration of a sweat test to rule out of confirm the diagnosis of cystic fibrosis. This article discusses, in a series of questions and answers, the currently available sweat testing methods and describes the various methods' reliability, limitations, and frequency of use. In addition, sweat testing utilization and the interpretation and evaluation of test results are discussed so that the clinician can critically analyze the laboratory data.