title: Precision and within- and between-day variation of bioimpedance parameters in children aged 2-14 years.
abstract: OBJECTIVE
  Bioimpedance spectroscopy (BIS) offers the possibility to perform rapid estimates of fluid distribution and body composition. Few studies, however, have addressed the precision and biological variation in a pediatric population. Our objectives were to evaluate precision, variation within- and between-days for the BIS-determined parameters total body fluid, extra-cellular fluid, intra-cellular fluid, body cell mass, fat-free mass, extra-cellular resistance, intra-cellular resistance and percentage body fat using a Xitron 4200.
  
  
  METHODS
  All 133 children (81 boys, 52 girls; 2.4-14.9 years) had one series measured on day one (precision population). Forty-four children had a second series on day one (within-day sub-population). Thirty-two children had a series measured on the next day (between-day sub-population). Each measurement series consisted of three repeated measurements. A linear mixed model was used for statistical analysis.
  
  
  RESULTS
  The precision was 0.3-0.8% in children ≥6 years and 0.5-2.4% in children <6 years with a statistically significant difference between the two age-groups (p<0.001). Within-day variation was 1.1-2.8% and between-day variation 2.4-5.7%. Total variation and reference change values are reported.
  
  
  CONCLUSIONS
  The Xitron 4200 has a very good but age-dependent precision. The median value of three repeated measurements is recommended in order to avoid incorrect measurements.
authors.affiliation: Department of Nuclear Medicine, Aalborg Hospital, Aarhus University Hospital, Aalborg, Denmark. tba@rn.dk
authors.forename: Trine B
authors.initials: TB
authors.lastname: Andersen
authors.forename: Lars
authors.initials: L
authors.lastname: Jødal
authors.forename: Anne
authors.initials: A
authors.lastname: Arveschoug
authors.forename: Anni
authors.initials: A
authors.lastname: Eskild-Jensen
authors.forename: Jørgen
authors.initials: J
authors.lastname: Frøkiær
authors.forename: Jens
authors.initials: J
authors.lastname: Brøchner-Mortensen
mesh_terms: D000273:Adipose Tissue / Q000254:growth & development; D000293:Adolescent; D041923:Adolescent Development; D000465:Algorithms; D001823:Body Composition; D001826:Body Fluids; D002648:Child; D002657:Child Development; D002675:Child, Preschool; D003718:Denmark; D058266:Dielectric Spectroscopy; D017097:Electric Impedance; D045604:Extracellular Fluid; D005260:Female; D006801:Humans; D007424:Intracellular Fluid; D008297:Male; D012016:Reference Values; D015203:Reproducibility of Results; D013223:Statistics as Topic