title: Quality of sweat test (ST) based on the proportion of sweat sodium (Na) and sweat chloride (Cl) as diagnostic parameter of cystic fibrosis: are we on the right way?
abstract: BACKGROUND
  To assess the quality of sweat test (ST) based on the proportion of sweat sodium and sweat chloride as diagnostic parameter of cystic fibrosis (CF).
  
  
  METHODS
  A retrospective study of 5,721 sweat samples and subsequent descriptive analysis were carried out. The test was considered "of good quality" (correct) when: (i) sweat chloride was lower than 60 mEq/L, and sweat sodium was higher than sweat chloride; (ii) sweat chloride was higher than 60 mEq/L, and sweat sodium was lower than sweat chloride.
  
  
  RESULTS
  The study included 5,692/5,721 sweat samples of ST which had been requested due to clinical presentations compatible with CF and/or neonatal screenings with altered immunoreactive trypsinogen values. Considering the proportion of sweat sodium and sweat chloride as ST quality parameter, the test was performed correctly in 5,023/5,692 (88.2 %) sweat samples. The sweat chloride test results were grouped into four reference ranges for chloride (i) chloride < 30 mEq/L: 3,651/5,692 (64.1 %); (ii) chloride ≥ 30 mEq/L to < 40 mEq/L: 652/5,692 (11.5 %); (iii) ≥ 40 mEq/L to < 60 mEq/L: 673/5,692 (11.8 %); (iv) ≥ 60 mEq/L: 716/5,692 (12.6 %). In the comparative analysis, there was no association between ST quality and: (i) symptoms to indicate a ST [respiratory (p = 0.084), digestive (p = 0.753), nutritional (p = 0.824), and others (p = 0.136)], (ii) sweat weight (p = 0.416). However, there was a positive association with: (i) gender, (ii) results of ST (p < 0.001), (iii) chloride/sodium ratio (p < 0.001), (iv) subject's age at the time of ST [grouped according to category (p < 0.001) and numerical order (p < 0.001)]. For the subset of 169 patients with CF and two CFTR mutations Class I, II and/or III, in comparative analysis, there was a positive association with: (i) sweat chloride/sodium ratio (p < 0.001), (ii) sweat chloride values (p = 0.047), (iii) subject's age at the time of the ST grouped by numerical order (p = 0.001).
  
  
  CONCLUSIONS
  Considering that the quality of ST can be assessed by levels of sweat sodium and sweat chloride, an increasing number of low-quality tests could be observed in our sweat samples. The quality of the test was associated with important factors, such as gender, CF diagnosis, and subjects' age.
authors: Department of Pediatrics, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.|Laboratory of Pulmonary Physiology, Center for Pediatrics Investigation, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.
authors: Alethéa Guimarães
authors: AG
authors: Faria
authors: Department of Pediatrics, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil. fernandolimamarson@hotmail.com.|Laboratory of Pulmonary Physiology, Center for Pediatrics Investigation, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil. fernandolimamarson@hotmail.com.|Department of Medical Genetics, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil. fernandolimamarson@hotmail.com.|Departamento de Pediatria, Faculdade de Ciências Médicas, Universidade Estadual de Campinas, Tessália Vieira de Camargo, 126, Barão Geraldo, Cidade Universitária Zeferino Vaz, CEP: 13083-887, Campinas, São Paulo, Brazil. fernandolimamarson@hotmail.com.
authors: Fernando Augusto Lima
authors: FA
authors: Marson
authors: Department of Pediatrics, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.
authors: Carla Cristina de Souza
authors: CC
authors: Gomez
authors: Department of Pediatrics, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.|Laboratory of Pulmonary Physiology, Center for Pediatrics Investigation, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.
authors: Maria Ângela Gonçalves de Oliveira
authors: MÂ
authors: Ribeiro
authors: Department of Pediatrics, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.|Laboratory of Pulmonary Physiology, Center for Pediatrics Investigation, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.
authors: Lucas Brioschi
authors: LB
authors: Morais
authors: Department of Pediatrics, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.|Laboratory of Pulmonary Physiology, Center for Pediatrics Investigation, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.
authors: Maria de Fátima
authors: MF
authors: Servidoni
authors: Department of Medical Genetics, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.
authors: Carmen Sílvia
authors: CS
authors: Bertuzzo
authors: Department of Otorhinolaryngology, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.
authors: Eulália
authors: E
authors: Sakano
authors: Department of Pediatrics, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.
authors: Maura
authors: M
authors: Goto
authors: Department of Clinical Medicine, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.
authors: Ilma Aparecida
authors: IA
authors: Paschoal
authors: Department of Clinical Medicine, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.
authors: Mônica Corso
authors: MC
authors: Pereira
authors: Department of Pediatrics, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.
authors: Gabriel
authors: G
authors: Hessel
authors: Department of Clinical Pathology, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.
authors: Carlos Emílio
authors: CE
authors: Levy
authors: Department of Pediatrics, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.
authors: Adyléia Aparecida Dalbo Contrera
authors: AA
authors: Toro
authors: Department of Pediatrics, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.
authors: Andressa Oliveira
authors: AO
authors: Peixoto
authors: Department of Pediatrics, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.
authors: Maria Cristina Ribeiro
authors: MC
authors: Simões
authors: Department of Pediatrics, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.
authors: Elizete Aparecida
authors: EA
authors: Lomazi
authors: Department of Pediatrics, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.
authors: Roberto José Negrão
authors: RJ
authors: Nogueira
authors: Department of Pediatrics, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.
authors: Antônio Fernando
authors: AF
authors: Ribeiro
authors: Department of Pediatrics, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.|Laboratory of Pulmonary Physiology, Center for Pediatrics Investigation, Faculty of Medical Sciences, University of Campinas, Campinas, Brazil.
authors: José Dirceu
authors: JD
authors: Ribeiro
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D002712:Chlorides / Q000032:analysis*; D003550:Cystic Fibrosis / Q000175:diagnosis*; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012964:Sodium / Q000032:analysis*; D013542:Sweat / Q000737:chemistry*; D055815:Young Adult
chemical_list: D002712:Chlorides; D012964:Sodium
keywords: Cystic fibrosis; Diagnosis; Electrolytes; Sweat