title: Repeatability and Diagnostic Value of Nasal Potential Difference in a Genetically Admixed Population.
abstract: BACKGROUND
  The genetic diversity of the Brazilian population results from three ethnic groups admixture: Europeans, Africans and Amerindians, thus increasing the difficulty of performing cystic fibrosis (CF) diagnosis. The nasal potential difference (NPD) evaluates the cystic fibrosis transmembrane conductance regulator (CFTR) and epithelial sodium channel (ENaC) activity. Despite being a useful CF diagnostic test and a biomarker of CFTR-modulator drugs, it is also highly operator dependent. Therefore, it may be difficult to get accurate results and to interpret them. Wilschanski and Sermet scores were proposed to address these issues. This study aimed to evaluate repeatability and diagnostic value of NPD parameters and Wilschanski and Sermet scores in a CF center in Rio de Janeiro.
  
  
  METHODS
  NPD was performed in 78 subjects. Maximal PD, amiloride response, total chloride response, and Wilschanski and Sermet scores were explored as means (confidence interval, CI). One-way ANOVA was used to compare mean differences and Scheffe test was used to pair-wise comparisons. Repeatability was evaluated by scatter and Bland-Altman plots. The Ethics Committee of the CF Center has approved the study protocol. Parents and adult participants signed an informed consent form.
  
  
  RESULTS
  Forty-eight healthy-volunteers, 19 non-CF and 11 CF patients were enrolled in this study. Significant differences were found when comparing CF patients' NPD parameters to the other two groups (P = 0.000). Moreover, no significant differences were found when parameters from non-CF patients were compared with those from healthy volunteers (P > 0.05). The means of NPD parameters and diagnostic scores of each group were in concordance with disease/non-disease conditions. The repeatability data - Wilschanski and Sermet and NPD - allow NPD to be performed in this Brazilian CF Center.
  
  
  CONCLUSIONS
  The present study gathered consistent data for Bland-Altman plots. The results of Wilschanski and Sermet diagnostic scores suggest that they were concordant with CF/non-CF conditions. More NPD tests should be performed in the Rio de Janeiro CF dynamic cohort to contribute to international NPD validation studies and to provide NPD as a biomarker in Brazil.
authors.affiliation: Pediatric Pulmonology, Pediatric Department, Fernandes Figueira National Institute of Woman, Child and Adolescent Health, Oswaldo Cruz Foundation/FIOCRUZ, Rio de Janeiro, Brazil.
authors.forename: Izabela Rocha
authors.initials: IR
authors.lastname: Sad
authors.affiliation: Pediatric Pulmonology, Pediatric Department, Fernandes Figueira National Institute of Woman, Child and Adolescent Health, Oswaldo Cruz Foundation/FIOCRUZ, Rio de Janeiro, Brazil.
authors.forename: Laurinda Yoko Shinzato
authors.initials: LY
authors.lastname: Higa
authors.affiliation: Louvain Center for Toxicology and Applied Pharmacology (LTAP), Institut de Recherche Experimentale et Clinique (IREC) Universite Catholique de Louvain, Brussels, Belgium.
authors.forename: Teresinha
authors.initials: T
authors.lastname: Leal
authors.affiliation: Pediatric Pulmonology, Pediatric Department, Fernandes Figueira National Institute of Woman, Child and Adolescent Health, Oswaldo Cruz Foundation/FIOCRUZ, Rio de Janeiro, Brazil.
authors.forename: Raisa da Silva
authors.initials: Rda S
authors.lastname: Martins
authors.affiliation: Laboratory of Quantitative Methods, Fernandes Figueira National Institute of Woman, Child and Adolescent Health, Oswaldo Cruz Foundation/FIOCRUZ, Rio de Janeiro, Brazil.
authors.forename: Ana Claudia
authors.initials: AC
authors.lastname: de Almeida
authors.affiliation: Clinical Research Unit, Fernandes Figueira National Institute of Woman, Child and Adolescent Health, Oswaldo Cruz Foundation/FIOCRUZ, Rio de Janeiro, Brazil.
authors.forename: Eloane Goncalves
authors.initials: EG
authors.lastname: Ramos
authors.affiliation: Laboratory of Human Genetics, Oswaldo Cruz Institute, Oswaldo Cruz Foundation/FIOCRUZ, Pavilhao Leonidas Deane, sala 611, Rio de Janeiro, Brazil.
authors.forename: Giselda Maria Kalil
authors.initials: GM
authors.lastname: de Cabello
authors.affiliation: Laboratory of Quantitative Methods, Fernandes Figueira National Institute of Woman, Child and Adolescent Health, Oswaldo Cruz Foundation/FIOCRUZ, Rio de Janeiro, Brazil.
authors.forename: Maria Virginia Marques
authors.initials: MV
authors.lastname: Peixoto
keywords: Cystic fibrosis; Diagnostic test; Nasal potential difference; Repeatability; Sermet score; Wilschanski index