title: Prevalence of hyponatremia at diagnosis and factors associated with the longitudinal variation in serum sodium levels in infants with cystic fibrosis.
abstract: OBJECTIVE
  To determine the prevalence of hyponatremia at diagnosis in patients with cystic fibrosis and identify the factors associated with changes in serum sodium concentration over time.
  
  
  METHODS
  This longitudinal study investigated whether variations in serum sodium concentration were associated with age, diet, infection status, and climate/temperature. Multivariate analysis was performed using the random-effects model for longitudinal data.
  
  
  RESULTS
  Hyponatremia at diagnosis was observed in 19 of the 20 patients (95%). Factors identified as associated with variations in serum sodium concentration were diet (P = .008) and climate/temperature (P = .005). Intake of solid foods appeared to greatly increase the serum sodium concentration (increase of 5 mEq/L after introduction of solid foods); however, a confounding factor between diet and age cannot be definitively ruled out. Climate/temperature contributed in an inverse way; a 1°C-increase in ambient temperature was associated with a 0.5-mEq/L decrease in serum sodium concentration.
  
  
  CONCLUSIONS
  Infants with cystic fibrosis who feed on breast milk or formula and live in a high-temperature environment are at increased risk for hyponatremia, even when receiving a higher salt intake in accordance with recommendations.
authors.affiliation: Department of Pediatrics, Diagnostic Support Action and Research Center, Faculty of Medicine/Universidade Federal de Minas Gerais, Belo Horizonte, Brazil. elizabet@medicina.ufmg.br
authors.forename: Elizabet V
authors.initials: EV
authors.lastname: Guimarães
authors.forename: Graziela C M
authors.initials: GC
authors.lastname: Schettino
authors.forename: Paulo A M
authors.initials: PA
authors.lastname: Camargos
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Penna
mesh_terms: D001942:Breast Feeding; D002675:Child, Preschool; D003550:Cystic Fibrosis / Q000097:blood* / Q000175:diagnosis; D005260:Female; D006801:Humans; D007010:Hyponatremia / Q000150:complications* / Q000628:therapy; D007223:Infant; D007225:Infant Food; D041943:Infant Formula; D008297:Male; D012964:Sodium / Q000097:blood*; D012965:Sodium Chloride / Q000008:administration & dosage; D014329:Tropical Climate
chemical_list: D012965:Sodium Chloride; D012964:Sodium